Merge pull request #10 from robhoes/master

Batch IP monitor changes for 1 second
Batch IP monitor changes for 1 second

IP address changes, e.g. as a result of DHCP, usually trigger multiple events
in the IP watcher. This change causes Xapi to be notified just once if multiple
events occur within a second.

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Do signal xapi when an IP address is removed

BobB pointed out that when a DHCP lease expires, the IP address may go away.
Therefore, a signal to xapi for it to update its DB makes sense.

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>