heat engine : watchrule don't run rule for every SampleCount

We should not be triggering a run_rule (which is an alarm action)
for every datapoint when the SampleCount statistic is specified,
otherwise e.g IHA instances get replaced every heartbeat signal!
run_rule should only be called in response to a rule evaluate(),
or an explicit override via set_watch_state()

ref bug 1100719

Change-Id: I91b144f24b542f48aa7fa98d8d8c404479e13483
Signed-off-by: Steven Hardy <shardy@redhat.com>