Don't install git-hg
Don't install git-hg

git-hg is obsoleted by git-remote-hg and no longer present on F22. We
don't use it as the repositories we use are git so instead of trying
to deal with two package names (centos and F22) just stop installing it.

Change-Id: I7835ec90d8bcbf1183b4217b9bc6d7714833d243
openstack/tripleo-common,openstack/tripleo-common