Allow runtime ordering of tests to be specified

Allow other plugins to specify tests to get run, and preserve the ordering of tests.

Currently, a plugin may set the "test" parameter with a comma separated list of tests to run.
However, the order is not preserved.

For plugins such as the maven-clover2-plugin, (possibly the maven-reactor-plugin?) that optimize the build/test run, ordering of a tests is a very nice way to ensure the build fails as fast as possible.