Revision 552376

HADOOP-1523 'Hung region servers waiting on write locks'
On shutdown, region servers and masters were just cancelling leases
without letting 'lease expired' code run -- code to clean up
outstanding locks in region server.  Outstanding read locks were
getting in the way of region server getting necessary write locks
needed for the shutdown process.  Also, cleaned up messaging around
shutdown so its clean -- no timeout messages as region servers try
to talk to a master that has already shutdown -- even when region
servers take their time going down.
M src/contrib/hbase/conf/hbase-default.xml
    Make region server timeout 30 seconds instead of 3 minutes.
    Clients retry anyways. Make so its likely region servers report
    in their shutdown message before their lease expires on master.
M src/contrib/hbase/src/java/org/apache/hadoop/hbase/Leases.java
    (closeAfterLeasesExpire): Added.
* src/contrib/hbase/src/java/org/apache/hadoop/hbase/HRegionServer.java
    Added comments.
    (stop): Converted from public to default access (master shuts
    down regionservers).
    (run): Use leases.closeAfterLeasesExpire instead of leases.close.
    Changed log of main thread exit from DEBUG to INFO.
* src/contrib/hbase/src/java/org/apache/hadoop/hbase/HMaster.java
    (letRegionsServersShutdown): Add better explaination of shutdown
    process to method doc.  Changed timeout waits from
    hbase.regionserver.msginterval to threadWakeFrequency.
    (regionServerReport): If closing, we used to immediately respond
    to region server with a MSG_REGIONSERVER_STOP.  This meant that
    we avoided handling of the region servers MSG_REPORT_EXITING sent
    on shutdown so region servers had no chance to cancel their lease
    in the master.  Reordered.  Moved sending of MSG_REGIONSERVER_STOP
    to after handling of MSG_REPORT_EXITING.  Also, in handling of
    MSG_REGIONSERER_STOP removed cancelling of leases.  Let leases
    expire normally (or get cancelled when the region server comes in
    with MSG_RPORT_EXITING).
* src/contrib/hbase/src/java/org/apache/hadoop/hbase/HMsg.java
    (MSG_REGIONSERVER_STOP_IN_ARRAY): Added.