Parameterizes test_se_message_echo over an editable list of TEST_ROOMs.

On the main branches, this list can remain as is so it works with
Manishbot. On my test branch, I'd also like to add Stack Overflow's
sandbox, and later MSO's too, so I can test that it's working on all
hosts.
Merge branch 'parameterized-test-rooms' into test

Conflicts:
	test/test_live_messages.py