Shave about 3sec off a regression test.
Add POE::Test::Sequence::create_generic_session().

A generic session runs all the events it receives through the test
sequence.  It seems like something that might be common for simple
tests.

t/90_regression/leolo-alarm-adjust.t uses it as a proof of concept, a
future documentation example, and to shave about 2sec off the test.