Updated release_public_ips and boot_instances
Updated release_public_ips and boot_instances

Comparing addr.instance_id with null string to verify available
address.

Added 4 second timeout in boot_instances() while checking for
instance status.

Signed-off-by: Shashank Sahni <48273395e0436587f8f1beebda52d256c947abb2@gmail.com>

siel-iiith/MultiStack,siel-iiith/MultiStack