Jenkins log when docker-test1 and docker-test2 DOES run in parallel:
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Nov 04, 2016 11:13:59 AM com.nirima.jenkins.plugins.docker.DockerCloud provision
INFO: Asked to provision 1 slave(s) for: docker-slave
Nov 04, 2016 11:13:59 AM com.nirima.jenkins.plugins.docker.DockerCloud provision
INFO: Will provision 'kkm', for label: 'docker-slave', in cloud: 'docker'
Nov 04, 2016 11:13:59 AM com.nirima.jenkins.plugins.docker.DockerCloud addProvisionedSlave
INFO: Provisioning 'kkm' number '0' on 'docker'; Total containers: '1'
Nov 04, 2016 11:13:59 AM hudson.slaves.NodeProvisioner$StandardStrategyImpl apply
INFO: Started provisioning Image of kkm from docker with 1 executors. Remaining excess workload: 0
Nov 04, 2016 11:13:59 AM com.nirima.jenkins.plugins.docker.DockerCloud provisionWithWait
INFO: Trying to run container for kkm
Nov 04, 2016 11:13:59 AM com.nirima.jenkins.plugins.docker.utils.PortUtils$ConnectionCheckSSH execute
INFO: SSH port is open on *.*.*.*:32791
Nov 04, 2016 11:13:59 AM com.nirima.jenkins.plugins.docker.launcher.DockerComputerSSHLauncher getSSHLauncher
INFO: Creating slave SSH launcher for /*.*.*.*:32791
Nov 04, 2016 11:14:02 AM hudson.slaves.NodeProvisioner$2 run
INFO: Image of kkm provisioning successfully completed. We have now 2 computer(s)
Nov 04, 2016 11:14:02 AM com.nirima.jenkins.plugins.docker.DockerCloud provision
INFO: Asked to provision 1 slave(s) for: docker-slave
Nov 04, 2016 11:14:02 AM com.nirima.jenkins.plugins.docker.DockerCloud provision
INFO: Will provision 'kkm', for label: 'docker-slave', in cloud: 'docker'
Nov 04, 2016 11:14:02 AM com.nirima.jenkins.plugins.docker.DockerCloud addProvisionedSlave
INFO: Provisioning 'kkm' number '1' on 'docker'; Total containers: '2'
Nov 04, 2016 11:14:02 AM hudson.slaves.NodeProvisioner$StandardStrategyImpl apply
INFO: Started provisioning Image of kkm from docker with 1 executors. Remaining excess workload: -0.427
Nov 04, 2016 11:14:02 AM com.nirima.jenkins.plugins.docker.DockerCloud provisionWithWait
INFO: Trying to run container for kkm
Nov 04, 2016 11:14:02 AM com.nirima.jenkins.plugins.docker.utils.PortUtils$ConnectionCheckSSH execute
INFO: SSH port is open on *.*.*.*:32792
Nov 04, 2016 11:14:02 AM com.nirima.jenkins.plugins.docker.launcher.DockerComputerSSHLauncher getSSHLauncher
INFO: Creating slave SSH launcher for /*.*.*.*:32792
[11/04/16 11:14:05] SSH Launch of docker-4969a4569388 on *.*.*.* completed in 2,880 ms
Nov 04, 2016 11:14:12 AM hudson.slaves.NodeProvisioner$2 run
INFO: Image of kkm provisioning successfully completed. We have now 3 computer(s)
[11/04/16 11:14:15] SSH Launch of docker-29c4aa8ae132 on *.*.*.* completed in 2,998 ms
Nov 04, 2016 11:14:20 AM hudson.model.Run execute
INFO: docker-test1 #25 main build action completed: SUCCESS
Nov 04, 2016 11:14:20 AM com.nirima.jenkins.plugins.docker.DockerSlave _terminate
INFO: Disconnected computer
Nov 04, 2016 11:14:20 AM hudson.remoting.SynchronousCommandTransport$ReaderThread run
SEVERE: I/O error in channel docker-4969a4569388
java.io.IOException: Unexpected termination of the channel
	at hudson.remoting.SynchronousCommandTransport$ReaderThread.run(SynchronousCommandTransport.java:73)
Caused by: java.io.EOFException
	at java.io.ObjectInputStream$PeekInputStream.readFully(ObjectInputStream.java:2353)
	at java.io.ObjectInputStream$BlockDataInputStream.readShort(ObjectInputStream.java:2822)
	at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:804)
	at java.io.ObjectInputStream.<init>(ObjectInputStream.java:301)
	at hudson.remoting.ObjectInputStreamEx.<init>(ObjectInputStreamEx.java:48)
	at hudson.remoting.AbstractSynchronousByteArrayCommandTransport.read(AbstractSynchronousByteArrayCommandTransport.java:34)
	at hudson.remoting.SynchronousCommandTransport$ReaderThread.run(SynchronousCommandTransport.java:59)

Nov 04, 2016 11:14:20 AM com.nirima.jenkins.plugins.docker.DockerSlave _terminate
INFO: Stopped container 4969a45693885b4f594c2f65a409ba19a0681487dd48a46ac2817affe33ff64c
Nov 04, 2016 11:14:20 AM com.nirima.jenkins.plugins.docker.DockerSlave _terminate
INFO: Shutdowned slave for 4969a45693885b4f594c2f65a409ba19a0681487dd48a46ac2817affe33ff64c
Nov 04, 2016 11:14:20 AM com.nirima.jenkins.plugins.docker.DockerSlave _terminate
INFO: Removed container 4969a45693885b4f594c2f65a409ba19a0681487dd48a46ac2817affe33ff64c
Nov 04, 2016 11:14:30 AM hudson.model.Run execute
INFO: docker-test2 #11 main build action completed: SUCCESS
Nov 04, 2016 11:14:30 AM com.nirima.jenkins.plugins.docker.DockerSlave _terminate
INFO: Disconnected computer
Nov 04, 2016 11:14:30 AM hudson.remoting.SynchronousCommandTransport$ReaderThread run
SEVERE: I/O error in channel docker-29c4aa8ae132
java.io.IOException: Unexpected termination of the channel
	at hudson.remoting.SynchronousCommandTransport$ReaderThread.run(SynchronousCommandTransport.java:73)
Caused by: java.io.EOFException
	at java.io.ObjectInputStream$PeekInputStream.readFully(ObjectInputStream.java:2353)
	at java.io.ObjectInputStream$BlockDataInputStream.readShort(ObjectInputStream.java:2822)
	at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:804)
	at java.io.ObjectInputStream.<init>(ObjectInputStream.java:301)
	at hudson.remoting.ObjectInputStreamEx.<init>(ObjectInputStreamEx.java:48)
	at hudson.remoting.AbstractSynchronousByteArrayCommandTransport.read(AbstractSynchronousByteArrayCommandTransport.java:34)
	at hudson.remoting.SynchronousCommandTransport$ReaderThread.run(SynchronousCommandTransport.java:59)

Nov 04, 2016 11:14:31 AM com.nirima.jenkins.plugins.docker.DockerSlave _terminate
INFO: Stopped container 29c4aa8ae132f941d96a457406f0c5349b5b3daebdf356537b3a180d6b89ca26
Nov 04, 2016 11:14:31 AM com.nirima.jenkins.plugins.docker.DockerSlave _terminate
INFO: Shutdowned slave for 29c4aa8ae132f941d96a457406f0c5349b5b3daebdf356537b3a180d6b89ca26
Nov 04, 2016 11:14:31 AM com.nirima.jenkins.plugins.docker.DockerSlave _terminate
INFO: Removed container 29c4aa8ae132f941d96a457406f0c5349b5b3daebdf356537b3a180d6b89ca26