Add assertions to test_reconstructor test_get_response
Add assertions to test_reconstructor test_get_response

Tighten up test to verify that 404 response results in a None
return from reconstructor _get_response. Merge this test case
into the test_get_response method to make use of the do_test()
infrastructure. Add check for 503 response status.

Also, use assertFalse to verify empty log lines, since a failure
will then result in any log lines being shown in failure message.

Related-Change: Iba86b495a14c15fc6eca8bf8a7df7d110256b0af
Co-Authored-By: Clay Gerrard <clay.gerrard@gmail.com>

Change-Id: Ia83517e6d4c2f5eeb136abd4c04ddab639d40b9e

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