BOTH strategy reallocating correctly

Fixes RM#2964
Merge pull request #180 from jkoelker/both_strat_bug_171

BOTH strategy reallocating correctly
Fixes #169

We were unnecessarily checking whether or not an IP was actually
allocated in the subnet_find_allocation_count check. The reality is we
only care if the IP has been generated before, not whether or not it's
actually been allocated. The reason is by the time check the counts in
the database, we've already failed our attempt to reallocate from one of
the subnets. If we assume that no IPs are available for reallocation,
the next step is finding a subnet we can generate a *new* IP address in.

Additionally, the patch takes the proactive step of deleting the
offending IP address altogether. Note that it only touches deallocated
and available IPs.