fix test of trebuchet provider

the provider expects a package name with <basedir>/<reponame>
so for example integration/phpcs (not just integration);
in the special case where the basedir and the repo subdir
name are the same the code will 'just work' but it's by luck,
not by design

Change-Id: I09479423b6428e5d16f59d6da0b4a2185b926fa3