Rollback quota in os_tenant_network

when we call API with 'os_tenant_networks' to delete an existing network
it might fail due to unexpected reason, we should rollback the
quota we reserved otherwise we will face no quota later.

Change-Id: Ic74a7a8df337070f17b1ea6916809fa93880a287
Closes-Bug: 1296489
Merge "Rollback quota in os_tenant_network"