Add simple script to setup mysql and postgresql databases, this script
can be run by users during testing and will be run by CI systems for
specific setup before running unit tests.
This allows to change in project-config the python-db jobs to
python-jobs since python-jobs will call this script initially.
Update CONTRIBUTING for this.
See also
http://lists.openstack.org/pipermail/openstack-dev/2016-November/107784.html
Change-Id: I3463e75057d0d4544f6a0212da888759ab5e171b
Needed-By: I92e6e6502c2c516babf2bf66f3514875f77c460e