Import run_cross_tests.sh from oslo-incubator

Replace the local version of run_cross_tests.sh with
the version in oslo-incubator.

Depends on https://review.openstack.org/#/c/83411/
and https://review.openstack.org/#/c/83412/

Change-Id: I3d3e25f92ab6337432b54967a381662f32902a6d