Update tempest test sample in devstack/README.md

As part of bp:tempest-repo-restructure, the scenario directory is added and
scenario tests are moved there. The tempest test sample should be updated
in README.md.

Fixes bug #1207109

Change-Id: I25067e4b42697985e8f4b808fad5eb801c805f9f
Run Neutron migrations after creating schema

Partial-Bug 1207402

This patch executes Neutron DB migrations (based on alembic)
before starting the Neutron services, similar to what happens
for most of other openstack projects managed by devstack.
This will ensure devstack always creates correctly version-stamped
Neutron databases.

Change-Id: Ia941c426a1563bcc4cb5eae64ea30c0bf7677220
Some bash versions don't support negative lengths

Fix to make the service string work on these versions of bash too

Change-Id: Ibb9868ea7bf44480be76a8ea9d7d9fbc278a8ef3
Re-enble pip -e in setup_develop

We had a bad merge somewhere along the way which reverted the pip -e
part of things. Replace it.

Change-Id: I620bea80eac7ad53b5bfb79dd2b21c29ad1b2267
Don't uninstall packages when on xenserver

It turns out our fix for package madness breaks when running on
xenserver. Put in a simple exclusion for that case until we figure out a
more total and systemic solution to everyone's problems.

Change-Id: I491917015337f83206937c53949a62aa63f4679f
Merge "Re-enble pip -e in setup_develop"
Merge "Update tempest test sample in devstack/README.md"
Merge "Run Neutron migrations after creating schema"
Merge "Some bash versions don't support negative lengths"
Merge "Don't uninstall packages when on xenserver"