Stop using cinder.exception from cinder.rpc.

Stop using cinder.exception from cinder.rpc.

This patch is a part of continuing to remove dependencies from cinder.rpc
on the rest of cinder.  One RPC related exception was defined in
cinder.exception, so that was moved to cinder.rpc.common where the rest of
them live.  These exceptions were changed to no longer use CinderException
as their base.  Instead, there is a new RPCException base.

One other change that should be reviewed closely is the removal of using
cinder.exception.wrap_exception() in cinder.rpc.amqp.  As far as I can tell,
this didn't actually do anything since nothing was being passed in to
wrap_exception().

Change-Id: I36ff7c05ab0467ad8506b56d561c532eadf8dff8
Reviewed-on: https://review.openstack.org/9899
Reviewed-by: Vish Ishaya <vishvananda@gmail.com>
Approved: John Griffith <john.griffith@solidfire.com>
Tested-by: Jenkins