Improve error logging for pygit2 SSH-based remotes
Improve error logging for pygit2 SSH-based remotes

If libgit2 is compiled without libssh2, an "Unsupported URL protocol"
GitError exception is raised. This commit catches this exception and, if
the credentials are a keypair (which means SSH auth), logs an meaningful
error message that will let the user know that libgit2 was probably not
compiled with libssh2.

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt