on ImportError set HAS_CEILCLIENT to false
Without this none of the watcher componenets can be started for master
as well as rocky because the ceilometercleint was deprecated.
Using the variable the support for ceilometer can be gradually removed
from master
A backport to rocky will allow using watcher without ceilometerclient.
Change-Id: I3beb0fb8f0a8e8e0a22acaf6bdeca492836bbee2