Fix test_changelog when git isn't globally setup.
Fix test_changelog when git isn't globally setup.

This test was assuming that it was possible to make a new git repo and
commit to it, but some versions of git will error if no user email is
set, and some users choose not to have that set globally.

Change-Id: I94401c4fe716021c2cb2f1585690463746c740c9

varunarya10/pbr,klmitch/pbr,JioCloud/pbr,klmitch/pbr,redhat-openstack/pbr,varunarya10/pbr,openstack-dev/pbr,JioCloud/pbr,WiFast/pbr,openstack-dev/pbr,WiFast/pbr,redhat-openstack/pbr,openstack-dev/pbr