git-client CLI implementation does not propogate username

I add the advanced behavior for submodules, and it fails to clone, as the slave does not use the correct credentials or username to clone the submodule

In addition, just to clone the base project, I am forced to use the username@ format of the ssh protocol, because the project does not specify this user from the credentials.

It probably needs to be inserted into the commands on the git-client plugin, though I am not sure exactly how to do this. The work-around solution for this is to modify the ssh_config on the host such that it knows the correct username/port/credentials for that hostname, but this is not very useful if i have to go customize tens or hundreds of slaves.