ATLINFR-3506: Support ancient version of git

Apparently git remote get-url is a relatively new addition to the library. This moves to something that was supported in git 1.8, which is the CentOS 7 default.

I have mixed feelings about expecting our code to support such a wide range of git versions: 1.8 saw its last patch over 5 years ago and a lot has changed since then. But CentOS 7 is going to be with us for a while, so we might as well make this fix.