tests: fix broken udp tests
tests: fix broken udp tests

test_udp_receive_bad_decoding was not asserting on anything to check
the deconding.

This change fixes that.

Change-Id: I87043dc19227eab74f5d5cd3a201c8fb8b4becea

openstack/ceilometer,ityaptin/ceilometer,openstack/ceilometer,ityaptin/ceilometer