* Use a more stable method to detect rosdep changes

The method for detecting rosdep changes in the repository checking
system doesn't seem to work very well under all circumstances, and
sometimes fails to determine the differences resulting in a failed job.

This change switches the test to use a line change detection mechanism
already in use in another test, so it should be more stable.

Reverts bdf1c621

* fixup! Use a more stable method to detect rosdep changes