Fix inconsistent usages for network resources

If a normal user created a fixed_ip/floating_ip, a usage record with
column `in_use=1` will be created in the quota_usages table, and if an
admin user deleted the resource, a new record with column `in_use=-1`
will be created..This will cause the quota for the resources not
released.

Fixes bug 1220727

Change-Id: I705f2f9ef327a3198da6a47df772c3a1a28e1b4e
Merge "Fix inconsistent usages for network resources"