[DOC] include call out of additional changed config defaults in 2.0 upgrade

Copied from feedback on HBASE-19158 from mdrob:

Default settings/configuration properties changed/renamed:

HBASE-19919
HBASE-19148
HBASE-18307
HBASE-17314
HBASE-15784
HBASE-15027
HBASE-14906
HBASE-14521

More detail later from mdrob:

would like to see notes that:

hbase.master.cleaner.interval changed from 1 min to 10 min
MasterProcedureConstants.MASTER_PROCEDURE_THREADS defaults to CPU/4 instead of CPU
hbase.rpc.server.nativetransport renamed to hbase.netty.nativetransport
hbase.netty.rpc.server.worker.count renamed to base.netty.worker.count
hbase.hfile.compactions.discharger.interval renamed to hbase.hfile.compaction.discharger.interval
hbase.hregion.percolumnfamilyflush.size.lower.bound removed at site level, but can still be applied at table level
hbase.client.reties.number now counts the total number of retries, not the total number of tries