This change updates the CI testing for git-review to test with Gerrit
3.4.4 and 3.7.1. This should give us good coverage of new and old Gerrit
behavior when making changes to git-review.
Note we leave 3.4.4 as the default in the test suite for local runs to
try and limit possibility of breaking old Gerrit when adding features to
git-review for new Gerrit.
Change-Id: I4a42eddec1e247cbb0af5e74b8f1cee0ad58a79a