Allow single test path to use '.' delimiter

Currently when running a single test with the surefire plugin. The path to the test has to be slash delimited
mvn -Dtest=org/test/MyTest

It would be convenient to be able to use the package name for the test like this:
mvn -Dtest=org.test.MyTest

The patch is a very simple change to replace the '.' with '/' in the plugin.