Fix bin/hbase thrift usage text

1. Thrift server usage text does not say anything about it requires a start or stop argument.
2. It ignores stop argument, it acts as the same as for start.

According to this comment:

// This is so complicated to please both bin/hbase and bin/hbase-daemon.
// hbase-daemon provides "start" and "stop" arguments
// hbase should print the help if no argument is provided

start and stop is just supported because bin/hbase-daemon, but hbase-daemon kills the process instead of calling it with a stop argument.