Some SubAlarm expressions can be evaluated immediately. If the
expression is MAX(m) > 10, a single measurement of m > 10 will cause
the SubAlarm to transition to the ALARM state regardless of any other
measurement of m that is received. However if the operater is < or <=,
MAX can't be immediately evaluated since a following measurement
could be larger than the one storeed. COUNT also can be evaluated
immediately if the operator is > or >= since it never decreases. MIN
is the opposite and can be immediately evaluated if the operator is
< or <=. AVG and SUM can't be evaluated until the end of the
evaluation window since the average or sum could go up or down
depending on the measurements received and whether or not they are
negative.
Also see if the sliding window for a SubAlarm can be slid when a
metric is received for the SubAlarm. This could allow the SubAlarm
to be evaluated faster than waiting for the tick tuple since that
is only received every 60 seconds.
Add unit tests for immediate SubAlarm evaluation.
Add unit tests for previously untested parts of SubAlarmStats
Change-Id: I989a82328fa4ccc04b49d203f70a1adc9fa4d3bb
96f9b442f3