add assert error information
add assert error information

There are the same error resp.status_int in different operators of
one function, then I can't point out which one returns this status_int.
Therefore, I assert error information.

Change-Id: I58bcba97a9f92e43e0f8ef26b801b69a6906af41

psachin/swift,redbo/swift,smerritt/swift,openstack/swift,swiftstack/swift,hurricanerix/swift,tipabu/swift,nadeemsyed/swift,hurricanerix/swift,psachin/swift,openstack/swift,matthewoliver/swift,nadeemsyed/swift,nadeemsyed/swift,matthewoliver/swift,hurricanerix/swift,redbo/swift,matthewoliver/swift,notmyname/swift,tipabu/swift,nadeemsyed/swift,clayg/swift,openstack/swift,swiftstack/swift,clayg/swift,smerritt/swift,notmyname/swift,clayg/swift,psachin/swift,clayg/swift,tipabu/swift,psachin/swift,openstack/swift,hurricanerix/swift,notmyname/swift,swiftstack/swift,smerritt/swift,smerritt/swift,tipabu/swift,matthewoliver/swift,notmyname/swift