Modify default slaves.sh to start apache-spark on MacOS

By default, Apache Spark sbin/start-all.sh will try to start worker using "ssh" to slave node, regardless we were testing using our laptop. Below modification is to start it using Bash instead of SSH.

Donghuas-MacBook-Air:sbin donghua$ diff slaves.sh slaves.sh.old

92,94c92,93

<       cmd="${@// /\\ } 2>&1"

<       echo $cmd

<       bash -c "$cmd"

---

>     ssh $SPARK_SSH_OPTS "$slave" $"${@// /\\ }" \

>       2>&1 | sed "s/^/$slave: /"

96,98c95,96

<       cmd="${@// /\\ } 2>&1"

<       echo $cmd

<       bash -c "$cmd"

---

>     ssh $SPARK_SSH_OPTS "$slave" $"${@// /\\ }" \

>       2>&1 | sed "s/^/$slave: /" &

Revised code could be found here:

https://github.com/luodonghua/bigdata/blob/master/slaves.sh

And modified version of spark-conf.sh to start multiple workers could be found here:

https://github.com/luodonghua/bigdata/blob/master/spark-config.sh