COLO: Implement the process of failover for primary VM

COLO: Implement the process of failover for primary VM

For primary side, if COLO gets failover request from users.
To be exact, gets 'x_colo_lost_heartbeat' command.
COLO thread will exit the loop while the failover BH does the
cleanup work and resumes VM.

Signed-off-by: zhanghailiang <[email protected]>
Signed-off-by: Li Zhijian <[email protected]>
Reviewed-by: Dr. David Alan Gilbert <[email protected]>
Reviewed-by: Amit Shah <[email protected]>
Signed-off-by: Amit Shah <[email protected]>