Allow Launcher to be applied Java options

Launcher is implemented as a Java application and sometimes I'd like to apply Java options.
One situation I have met is the time I try to attach debugger to Launcher.

Launcher is launched from bin/spark-class but there is no room to apply Java options.

build_command() {
  "$RUNNER" -Xmx128m -cp "$LAUNCH_CLASSPATH" org.apache.spark.launcher.Main "$@"
  printf "%d\0" $?
}

Considering that it's not so many times to apply Java options to Launcher, one compromise would just modify spark-class by user like as follows.

build_command() {
  "$RUNNER" -Xmx128m $SPARK_LAUNCHER_OPTS -cp "$LAUNCH_CLASSPATH" org.apache.spark.launcher.Main "$@"
  printf "%d\0" $?
}

But it doesn't work when any text related to Java options is output to standard output because whole output is used as command-string for spark-shell and spark-submit in current implementation.

One example is jdwp. When apply agentlib option to use jdwp for debug, we will get output like as follows.

Listening for transport dt_socket at address: 9876

The output shown above is not a command-string so spark-submit and spark-shell will fail.

To enable Java options for Launcher, we need treat command-string and others.