Only deallocate ips currently allocated

* Make the exception handler only remove currently allocated
  ips so that a second run won't remove reserved ips previously
  allocated.
* Also some pylint cleanup

Change-Id: I10359a69a2d9900fb6335ea0c459907b8e8f6189
Signed-off-by: Rosario Di Somma <rosario.disomma@dreamhost.com>