HBASE-25836 RegionStates#getAssignmentsForBalancer should only care about OPEN or...

HBASE-25836 RegionStates#getAssignmentsForBalancer should only care about OPEN or OPENING regions (#3219)

RegionStates#getAssignmentsForBalancer is used by the HMaster to
collect all regions of interest to the balancer for the next chore
iteration. We check if a table is in disabled state to exclude
regions that will not be of interest (because disabled regions are
or will be offline) or are in a state where they shouldn't be
mutated (like SPLITTING). The current checks are not actually
comprehensive.

Filter out regions not in OPEN or OPENING state when building the
set of interesting regions for the balancer to consider. Only
regions open (or opening) on the cluster are of interest to
balancing calculations for the current iteration. Regions in all
other states can be expected to not be of interest – either offline
(OFFLINE, or FAILED_*), not subject to balancer decisions now
(SPLITTING, SPLITTING_NEW, MERGING, MERGING_NEW), or will be
offline shortly (CLOSING) – until at least the next chore
iteration.

Add TRACE level logging.

Signed-off-by: Bharath Vissapragada <bharathv@apache.org>
Signed-off-by: Duo Zhang <zhangduo@apache.org>
Signed-off-by: Viraj Jasani <vjasani@apache.org>