Don't raise `DoesNotExist` on claims deletion
Don't raise `DoesNotExist` on claims deletion

We don't raise DoesNotExist when the queue that a claim has to be
deleted from does not exist.

Implements blueprint: sql-storage-driver

Change-Id: I2a3e11d493b066c5dae7af81db81989468e90726

openstack/zaqar,rackerlabs/marconi,openstack/zaqar,openstack/zaqar,openstack/zaqar