I'm using the Cloudbees Docker Build and Publish plugin, but when I specify a remote Docker host for image building and pushing, seems that it still tries to use the local docker cmd.

For example, I have a docker host running at http://myhost.com:4243 without credentials, I specified the Docker Host URI to be http://myhost.com:4243, but the build fails with error,

```
ERROR: Cannot run program "docker" (in directory "/var/jenkins_home/sharedspace"): error=2, No such file or directory
java.io.IOException: Cannot run program "docker" (in directory "/var/jenkins_home/sharedspace"): error=2, No such file or directory
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1048)
at hudson.Proc$LocalProc.<init>(Proc.java:244)
at hudson.Proc$LocalProc.<init>(Proc.java:216)
at hudson.Launcher$LocalLauncher.launch(Launcher.java:815)
at hudson.Launcher$ProcStarter.start(Launcher.java:381)
at com.cloudbees.dockerpublish.DockerBuilder$Perform.executeCmd(DockerBuilder.java:487)
at com.cloudbees.dockerpublish.DockerBuilder$Perform.executeCmd(DockerBuilder.java:431)
at com.cloudbees.dockerpublish.DockerBuilder$Perform.buildAndTag(DockerBuilder.java:373)
at com.cloudbees.dockerpublish.DockerBuilder$Perform.exec(DockerBuilder.java:311)
at com.cloudbees.dockerpublish.DockerBuilder$Perform.access$100(DockerBuilder.java:291)
at com.cloudbees.dockerpublish.DockerBuilder.perform(DockerBuilder.java:262)
```

My plugin version is 1.3.2