Fixes Redmine #530

Adds another clear_addresses call to the IP allocation logic to ensure
that we always clear up any policy excluded IPs before iterating to the
next available IP block.

Change-Id: I9e6a333547000c7dc42e463a3e5113786714a93d
Merge pull request #37 from Cerberus98/clear_addresses

Fixes Redmine #530