Improve fallback to master branch

If a change to a stable branch follows a change to the master branch
but a project does not have a stable branch, the workspace setup
falls back to checking out the master branch.  However, it checks
out the actual current master branch rather than the proposed future
state of the master branch as determined by Zuul.  This change will
cause d-g to look for a Zuul ref for the master branch if it decides
to fall back.

Change-Id: Idadb0e0c4cd9cb120ec2c55f16282fc66076a61d
Conditionally override PyPI for reqs integration

* devstack-vm-gate-wrap.sh: In preparation for performing
integration testing of the openstack/requirements global list on
changes to requirements and jeepyb/pypi-mirror, allow the
combination of ZUUL_PROJECT and DEVSTACK_GATE_REQS_INTEGRATION
envvars to determine whether to override the PyPI URL and use the
openstack mirror.

Change-Id: I21fe53b7a17594f1d7f20f1407d0c19d11ad11be
Revert "Revert "Enable q-vpn service""

The neutron issue is ws probably realted the native mysql client
library is not eventlet friendly without additional code change.

See also: 21bf6f7e4945bc7e8c303273ad10c28b6cfc8b08 (neutron)

This reverts commit 71baa816918d8ed29e1891edb3b511e3d9532280.

Change-Id: Ic4e4d007309fb4e95b36f8dd144b5676810b012a
Merge "Improve fallback to master branch"
Merge "Revert "Revert "Enable q-vpn service"""
Merge "Conditionally override PyPI for reqs integration"