Don't use 'git remote get-url', which is a new-ish feature.

Apparently most Mac's have git 2.6.2, which doesn't have this
feature.

This only affects end developers, so there's no urgency to push
this out to the bots.

TBR=agable@chromium.org,wkorman@chromium.org
BUG=
NOTRY=true

Review URL: https://codereview.chromium.org/1777043002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299185 0039d316-1c4b-4281-b951-d872f2087c98

git_cl.py

@@ -631,7 +631,7 @@ class Settings(object):
 
   def GetGitMirror(self, remote='origin'):
     """If this checkout is from a local git mirror, return a Mirror object."""
-    local_url = RunGit(['remote', 'get-url', remote]).strip()
+    local_url = RunGit(['config', '--get', 'remote.%s.url' % remote]).strip()
     if not os.path.isdir(local_url):
       return None
     git_cache.Mirror.SetCachePath(os.path.dirname(local_url))