Rename quantum to neutron.

Change-Id: Ibacb9ef23b6b0f4480575139d4915b13c5a6b3ea
Add provision config for 'service_available'.

 * tempest.conf has a new section called 'service_available' that
   indicates the availability for testing of each service
   individually.  Previously only neutron availability was
   configurable.

Change-Id: I6967a76deb7314eb8770e655b6d5562c661183e3