Service object that is passed to any launcher must implement
the following methods:
* start
* stop
* wait
* reset
Introducing abstract base class from which all openstack
services that use common.service code can subclass guarantees it.
Added documentation for launcher classes in service.py
Change-Id: I79b38a354dd85f58a7c16b34661bff02d9170a9f
Closes-Bug: #1447965