Clearer debug when test_terminate_sigterm fails.

Change-Id: I284583fa8a250cc08c571251fbcce5da57db9f13
Make failures in the periodic tests more detailed.

The current tests are very opaque when something fails. This change makes the
failure easier to understand without a debugger. The testtools version is
bumped to get a new HasLength matcher.

Change-Id: Iceafa70f88a8cc31a1b0ba912fe32a9fef1b2f18
Merge "Clearer debug when test_terminate_sigterm fails."
Merge "Make failures in the periodic tests more detailed."