scripts: process empty string in arguments

Examples:
 # scripts/scylla-jmx -l /usr/lib/scylla/jmx ""
 Result: script stuck

 # scripts/scylla-jmx "" -l /usr/lib/scylla/jmx
   Unknown parameter: /usr/lib/scylla/jmx
 Result: wrongly shift arguments

Above two problem caused by a redundant argument parse ("$PARAM_PORT"),
the variable isn't set, so it's a covert empty string. The others valid
9 options are all parsed with right case, and API_ADDR also be set by
other case path, so it's safe to remove $PARAM_PORT.

This patch removed the redundant argument, and skipped empty string in
arguments.

Signed-off-by: Amos Kong <amos@scylladb.com>
Message-Id: <74c3f75d58bab1a8348f2c87f58825eed4c5b705.1510501133.git.amos@scylladb.com>

scripts/scylla-jmx

@@ -63,10 +63,6 @@ do
       API_ADDR="-Dapiaddress="$2
       shift 2
       ;;
-    "$PARAM_PORT")
-      API_ADDR=$2
-      shift 2
-      ;;
     "$PARAM_JMX_PORT")
       JMX_PORT=$2
       shift 2