Make TRIBITS_CTEST_DRIVER() correctly report git update failures in extra repos

[bartlettroscoe]

This story is a follow-on to story #278. This story is to update the TRIBITS_CTEST_DRIVER() function to correctly report clone and update failures for the extra repos and then to abort doing anything further if that happens.

Implementation ideas

To do this, the logic that updates the extra repos really needs to executed inside of the ctest_update() command in the running of the cmake -P tribits_ctest_update_commands.cmake script. Doing that should not be that hard but we would need to pass in the needed info about the extra repos to be updated. The other advantage of this approach is that if the update fails, we will get a log of the commands run uploaded to CDash as a notes file.