Updated openstack/openstack
Project: openstack-infra/devstack-gate  3875417fd94fa52d6bfca87c548462321f15f125

Rename config => system-config in devstack-gate

The openstack-infra/config repo has been renamed to
openstack-infra/system-config. This patch edits devstack-gate
doc file.

Change-Id: I55eaf754f43be8fe273e8d4d591d18b73880a913