Do not force unit tests to be run while the rook repo is in the GOPATH. Now that Rook uses go modules, this is no longer necessary. Allow this by creating a helper function that unit tests can use that return the on-host path to the `rook` project root. Followup of https://github.com/rook/rook/pull/7119/commits/15a487cd5aa5d4dc59bc15ef610cb182257d9287 Signed-off-by: Sébastien Han <seb@redhat.com>