Install which if its not installed in base
Install which if its not installed in base

Some variants of RHEL containers are missing the 'which' command.
Percona's software used by mariadb depends on which, but doesn't have
a hard dependency requirement since it is usually installed in the
distribution.  To make mariadb work multinode on RHEL, install which
all the time for RPM distros.

Change-Id: I2c6aaa77a1fc8b7028b658a0dfd1935c1f1d738e
Partially-Implements: blueprint rhel-based-image-support

tonyli71/kolla,mrangana/kolla,dardelean/kolla-ansible,dardelean/kolla-ansible,coolsvap/kolla,toby82/kolla,rajalokan/kolla,limamauricio/mykolla,mandre/kolla,toby82/kolla,mandre/kolla,coolsvap/kolla,rahulunair/kolla,limamauricio/mykolla,fdumpling/kolla,openstack/kolla,coolsvap/kolla,openstack/kolla,fdumpling/kolla,rajalokan/kolla,stackforge/kolla,negronjl/kolla,limamauricio/mykolla,GalenMa/kolla,GalenMa/kolla,stackforge/kolla,nihilifer/kolla,intel-onp/kolla,stackforge/kolla,fdumpling/kolla,negronjl/kolla,rahulunair/kolla,mrangana/kolla,negronjl/kolla,dardelean/kolla-ansible,tonyli71/kolla,nihilifer/kolla,mandre/kolla,rajalokan/kolla,toby82/kolla,intel-onp/kolla