Update devstack to work with new split neutron services repos

This commit udpates devstack to work with the latest neutron services, which
are now in their own repositories. This will also unblock third party CI for
services testing. This also allows devstack users to run neutron with
services again.

Change-Id: I9cdd51f09edaccf218988240b48ce733d5771a65
Tempest: configure exact set of extensions to test

So far devstack configures tempest either for testing all extensions
or a specific subset. It does not allow users for specifying a set
of extensions which should not be exercised.

This patch adds this support. To this aim, the tempest configuration
process will scan API endpoints for active extensions using the
verify_tempest_config.py tool, and then will remove those extensions
which have been explicitly disabled by the user.

If an explicit subset of extensions to enable is passed to devstack,
tempest will use this subset, rather than the list of active
extensions.

Implements blueprint branchless-tempest-extensions

Change-Id: I263bcf04668953f414a4ef18cb98c1c373e142ad
add shebang lines to all lib files

With gerrit 2.8, and the new change screen, this will trigger syntax
highlighting in gerrit. Thus making reviewing code a lot nicer.

Change-Id: Id238748417ffab53e02d59413dba66f61e724383
Merge "Tempest: configure exact set of extensions to test"
Merge "add shebang lines to all lib files"
Merge "Update devstack to work with new split neutron services repos"
Merge commit 'refs/changes/34/140634/1' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch