Updated JGitWrapper to insert username in URL

JGit was attempting SSH login as root, ignoring what I specified in the username field. From what I've gathered, the SshSessionFactory is used only if the URL contains a username. I added support for handling that issue as well as URL syntax validation.

References:
https://jira.atlassian.com/browse/BAM-7665
http://stackoverflow.com/questions/23692747/specifying-ssh-key-for-jgit