Created Gerrit groups are self owned.

* jeepyb/cmd/manage_projects.py: When creating Gerrit groups do not set
an explicit owner so that the new groups are self owned.

Fixes bug 1178022

Change-Id: I343ff5b7a4040149caa13b07bc69f15b3086225f
Reviewed-on: https://review.openstack.org/35171
Reviewed-by: Elizabeth Krumbach Joseph <lyz@princessleia.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins