ssh: redirect git ssh to git-ssh

ssh: redirect git ssh to git-ssh

Since d26c5b1f67af8a4f (git-svn: provide an SVN_SSH script,
2018-02-08), Girocco has been redirecting any svn ssh commands through
a wrapper script that causes them to use Girocco's config file so that
various ssh options more conducive to batch use can be activated.

It has been doing this by setting and exporting the SVN_SSH environment
variable.

Now extend this by additionally setting the GIT_SSH variable too (like
it should have been in the first place) and renaming the wrapper to
a slightly more generic name at the same time.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>