Previously we mounted /etc/timezone if the kolla_base_distro is debian
or ubuntu. This would fail prechecks if debian or ubuntu images were
deployed on CentOS. While this is not a supported combination, for
correctness we should fix the condition to reference the host OS rather
than the container OS, since that is where the /etc/timezone file is
located.

Change-Id: Ifc252ae793e6974356fcdca810b373f362d24ba5
Closes-Bug: #1882553