We had ssh logic sprinkled between two git modules, and neither was
quite the right home for it. This largely moves the logic as-is to
its new home. We'll leave major refactoring to followup commits.
Bug: https://crbug.com/gerrit/12389
Change-Id: I300a8f7dba74f2bd132232a5eb1e856a8490e0e9
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/305483
Reviewed-by: Chris Mcdonald <cjmcdonald@google.com>
Tested-by: Mike Frysinger <vapier@google.com>
