[SPARK-28164] Fix usage description of start-slave.sh

## What changes were proposed in this pull request?

updated the usage message in sbin/start-slave.sh.
<masterURL> argument moved to first

## How was this patch tested?
tested locally with
Starting master
starting slave with (./start-slave.sh spark://<IP>:<PORT> -c 1
and opening spark shell with ./spark-shell --master spark://<IP>:<PORT>

Closes apache#24974 from shivusondur/jira28164.

Authored-by: shivusondur <[email protected]>
Signed-off-by: Sean Owen <[email protected]>

Author: shivusondur

sbin/start-slave.sh

@@ -40,7 +40,7 @@ fi
 CLASS="org.apache.spark.deploy.worker.Worker"
 
 if [[ $# -lt 1 ]] || [[ "$@" = *--help ]] || [[ "$@" = *-h ]]; then
-  echo "Usage: ./sbin/start-slave.sh [options] <master>"
+  echo "Usage: ./sbin/start-slave.sh <master> [options]"
   pattern="Usage:"
   pattern+="\|Using Spark's default log4j profile:"
   pattern+="\|Started daemon with process name"