Add support for tuskar-api service

Adds initial support for configuring and starting the tuskar-api
service.

To enable, add the following to your localrc:

enable_service tuskar
enable_service tuskar-api

The aim of this addition is to provide a more accessible (non devtest)
way for developers to run up tuskar in a familiar devstack environment.

See the official repos for more information:
https://github.com/openstack/tuskar/
https://github.com/openstack/python-tuskarclient

Change-Id: Id0c3c0d3a38100c66dbe6e3adf1f715162f99742
Merge "Add support for tuskar-api service"