Allow for checking out pull requests by number.

This should work with the -c argument of the cp-test command.  For
example, "cp-test -c origin/pull/123"
Clean up before exiting docker testing.

This prevents bind mounts from ending up with files created by Docker
that are owned by root.

Also, run everything in the project root.  This will allow buildr
artifacts and buildr clean to download and clean for every project.
Revert "Add oracle options to the cp-test docker script."

This reverts commit 2d714b33768cd3e79a1eade1b97e114bc2908bb1.

Instead of providing an option, we set ORACLE=1 in the .candlepinrc
file of the Oracle container.