fix: update rcov to simplecov

This commit replaces the :rcov task, which previously invoked rcov,
with the :coverage task, which invokes simplecov. Rcov does not work
with Ruby 1.9 and above.

Change-Id: If1188e7208e5a17cfafbf6b2154ffabbc6a0a0d8
adding arbitrary run list groups and ordering

Change-Id: I4d0ac7affc31f9bc57c1e5c5a5b5047689c0a205
adding some tests for run list items and shuffling old ones around

Change-Id: Id16024bbff9b52d03cb25b4e5ceeb10bc85966fa
ensuring that old-style :first, :last, :normal still work

Change-Id: Ie2ef78223ef507dbcacea919c4f2b54a3b28a81c