Explicitly manage common clock client lifetimes.

Change the CCHelper class to be an instanced instead of a static
pattern.  The CCHelper instances all share an interface to the common
clock service and register/unregister a callback handler in response
to there being CCHelper instance in the system or not.  This brings
usage of the CCHelper into like with the new auto-disable
functionality of the common time service.  For any given process,
whenever there are CCHelper instances active, the process will
maintain a callback target to the common clock service and will be
considered to be an active client.

Also change all of the users of the CCHelper interface to manage the
lifecycle of their new CCHelper instances.

Change-Id: I7c28c5d70d9b07ba7407b4ac706e7e7d7253001b