heat tools : openstack script install mysql via openstack-db

heat tools : openstack script install mysql via openstack-db

Don't install mysql-server in tools/openstack, instead allow
openstack-db to non-interactively install it for us, which means
the root password is set as per the -r password option when
installing on a fresh system with no mysql

NOTE : if testing this on a system which has had mysql installed,
do yum remove mysql-server && rm -fr /var/lib/mysql or the
reinstalled mysql will use the old credentials

fixes bug 1133502

Change-Id: Ie3ba56e5f971e032be4f099e81cbb24afe76dfbc