Bulk assignment: regionserver optimization by using a temporary cache for table descriptors when receveing an open regions request

During the assignment, on the regionserver, before creating the handlers we load the table description. Even if there is a cache, we check the timestamps for each region, while it's not necessary. The test below is just with one node, with more nodes the benefit will improve. By limiting the time spent in HRegion#openRegion we increase the parallelization during cluster startup, as the master is using a pool of threads to call the RS.

– Without the fix
2012-05-14 11:40:52,501 DEBUG org.apache.hadoop.hbase.master.AssignmentManager: Bulk assigning 1193 region(s) to localhost,11003,1336988444043
2012-05-14 11:41:09,947 DEBUG org.apache.hadoop.hbase.master.AssignmentManager: Bulk assigning done for localhost,11003,1336988444043

– With the fix
2012-05-14 11:34:40,444 DEBUG org.apache.hadoop.hbase.master.AssignmentManager: Bulk assigning 1193 region(s) to localhost,11003,1336988444043
2012-05-14 11:34:40,929 DEBUG org.apache.hadoop.hbase.master.AssignmentManager: Bulk assigning done for localhost,11003,1336988065948