Disable broxygen when running unit tests (except for the tests that use
broxygen). On my dual-core MacBook Pro, this change results in the
unit tests taking about 13% less time to finish running.
Tests that load "frameworks/communication/listen" must be serialized
to prevent other tests failing due to multiple Bro instances trying
to listen on the same port.
The dump-events.bro generates output that would show in the Broxygen
all-script tests. Suppressing that manually in the test for lack of a
better idea.