cannot use SSH credentials from within shell script build step.

Steps to reproduce:

1) Add SSH credential to jenkins for some site.

2) Configure a GIT repo to be checked out via the Jenkins process.

NOTE: This step works, no problem.

3) Create a build step (execute bash script) that performs the same check out using the same URL

In the shell script, add a single line:  "git clone URL  SOMEDIR" 

This should - work because the AGENT has been told to provide the credentials.

Expected: The GIT clone should work

Result: The GIT operation fails

Please note: this is a very simple test case/example that I have reduced from a much larger far more complex series of scripts.

NOTE: the SSH key does not require a pass phrase.

See below for the log output from Jenkins

[EnvInject] - Loading node environment variables.
Building remotely on myslave - tiopbld (tiop_linux) in workspace /scratch/jenkins/workspace/pybuilder-testing/shellscript_test.sh
[ssh-agent] Looking for ssh-agent implementation...
[ssh-agent] Exec ssh-agent (binary ssh-agent on a remote machine)
$ ssh-agent
SSH_AUTH_SOCK=/tmp/ssh-PRUTedOo0d7o/agent.16607
SSH_AGENT_PID=16609
[ssh-agent] Started.
$ ssh-add /scratch/jenkins/workspace/pybuilder-testing/shellscript_test.sh@tmp/private_key_2048740533538871194.key
Identity added: /scratch/jenkins/workspace/pybuilder-testing/shellscript_test.sh@tmp/private_key_2048740533538871194.key (/scratch/jenkins/workspace/pybuilder-testing/shellscript_test.sh@tmp/private_key_2048740533538871194.key)
[ssh-agent] Using credentials tiopbld
Cloning the remote Git repository
Cloning repository ssh://git@bitbucket.myserver.com/pybuild/pythonbuilder.git
{{ > git init /scratch/jenkins/workspace/pybuilder-testing/shellscript_test.sh # timeout=10}}
Fetching upstream changes from ssh://git@bitbucket.myserver.com/pybuild/pythonbuilder.git
{{ > git --version # timeout=10}}
using GIT_SSH to set credentials jenkins-tiop-myuser
{{ > git fetch --tags --progress ssh://git@bitbucket.myserver.com/pybuild/pythonbuilder.git +refs/heads/:refs/remotes/origin/}}
{{ > git config remote.origin.url ssh://git@bitbucket.myserver.com/pybuild/pythonbuilder.git # timeout=10}}
{{ > git config --add remote.origin.fetch +refs/heads/:refs/remotes/origin/ # timeout=10}}
{{ > git config remote.origin.url ssh://git@bitbucket.myserver.com/pybuild/pythonbuilder.git # timeout=10}}
Fetching upstream changes from ssh://git@bitbucket.myserver.com/pybuild/pythonbuilder.git
using GIT_SSH to set credentials jenkins-tiop-myuser
{{ > git fetch --tags --progress ssh://git@bitbucket.myserver.com/pybuild/pythonbuilder.git +refs/heads/:refs/remotes/origin/}}
{{ > git rev-parse refs/remotes/origin/master^{commit} # timeout=10}}
{{ > git rev-parse refs/remotes/origin/origin/master^{commit} # timeout=10}}
Checking out Revision 5255667cfed01bdfcecc558a2c63bd6679503fc7 (refs/remotes/origin/master)
{{ > git config core.sparsecheckout # timeout=10}}
{{ > git checkout -f 5255667cfed01bdfcecc558a2c63bd6679503fc7}}
Commit message: "test commit from new linus machine"
First time build. Skipping changelog.
[shellscript_test.sh] $ /bin/sh -xe /tmp/jenkins2668814567868620035.sh
+ git clone ssh://git@bitbucket.myserver.com/pybuild/pythonbuilder.git OUTPUTDIR
Cloning into 'OUTPUTDIR'...
Permission denied (publickey).
fatal: Could not read from remote repository.Please make sure you have the correct access rights
and the repository exists.
Build step 'Execute shell' marked build as failure
$ ssh-agent -k
unsetenv SSH_AUTH_SOCK;
unsetenv SSH_AGENT_PID;
echo Agent pid 16609 killed;
[ssh-agent] Stopped.
Unable to connect to Elasticsearch service. Check Elasticsearch is running in the correct namespace
Finished: FAILURE