Fixes bug 1076831
Previously we passed these credentials to the ceilometer central
agent via the OS_* environment variables.
Since these credentials are now needed by the compute agent also,
and have already leaked into the config file to enable the keystone
auth token middleware, we now switch over to using the config file
only and drop the environment variable usage.
Change-Id: I0298d711905a99aa5355fe034bb0e51e53b3be21
14246ac16b