Addressing https://issues.apache.org/jira/browse/SPARK-11218, mostly copied start-thriftserver.sh.
```
charlesyeh-mbp:spark charlesyeh$ ./sbin/start-master.sh --help
Usage: Master [options]

Options:
  -i HOST, --ip HOST     Hostname to listen on (deprecated, please use --host or -h)
  -h HOST, --host HOST   Hostname to listen on
  -p PORT, --port PORT   Port to listen on (default: 7077)
  --webui-port PORT      Port for web UI (default: 8080)
  --properties-file FILE Path to a custom Spark properties file.
                         Default is conf/spark-defaults.conf.
```
```
charlesyeh-mbp:spark charlesyeh$ ./sbin/start-slave.sh
Usage: Worker [options] <master>

Master must be a URL of the form spark://hostname:port

Options:
  -c CORES, --cores CORES  Number of cores to use
  -m MEM, --memory MEM     Amount of memory to use (e.g. 1000M, 2G)
  -d DIR, --work-dir DIR   Directory to run apps in (default: SPARK_HOME/work)
  -i HOST, --ip IP         Hostname to listen on (deprecated, please use --host or -h)
  -h HOST, --host HOST     Hostname to listen on
  -p PORT, --port PORT     Port to listen on (default: random)
  --webui-port PORT        Port for web UI (default: 8081)
  --properties-file FILE   Path to a custom Spark properties file.
                           Default is conf/spark-defaults.conf.
```

Author: Charles Yeh <charlesyeh@dropbox.com>

Closes #9432 from CharlesYeh/helpmsg.