Add clean handling of Control-C to the test suite

Add clean handling of Control-C to the test suite

Interrupting the test suite will noe run all cleanup necessary, (such
as terminating the child processes that are still actively listening
to empathy event streams), and will give a (partial) test report of
all tests that have been completed.

This is convenient for when a user doesn't want to wait for the slow
tests to complete, but can still get some good information from
sumarizing the results of all of the fast tests that have already been
performed.