Clean up get_instance_id_by_floating_address

Reduce number of nova.db calls in get_instance_id_by_floating_address
to 1, fixed_ip_get_by_floating_address (A new nova.db.api function)

Change-Id: Ie1313ea73290ae11dce03d3726d5c23e4d73cb00
Reduce number of iptable-save restore loops

Instead of running iptables-save and iptables-restore per table,
run iptables save and restore on all tables at once.

Change-Id: If610d07c22ddaeb03ab37ee64d3d3a55d5e5b34f
Merge "Clean up get_instance_id_by_floating_address"
Merge "Reduce number of iptable-save restore loops"