qga: group agent init/cleanup init separate routines

qga: group agent init/cleanup init separate routines

This patch better separates the init/cleanup routines out into
separate functions to make the start-up procedure a bit easier to
follow. This will be useful when we eventually break out the actual
start/stop of the agent's main loop into separates routines that
can be called multiple times after the init phase.

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>