scripts: dev_cli.sh: print help if command unspecified

To improve user friendliness, print help text when no command is given.

Signed-off-by: Ruslan Mstoi <ruslan.mstoi@intel.com>

scripts/dev_cli.sh

@@ -168,6 +168,7 @@ process_volumes_args() {
         exported_volumes="$exported_volumes --volume $var"
     done
 }
+
 cmd_help() {
     echo ""
     echo "Cloud Hypervisor $(basename "$0")"
@@ -625,6 +626,12 @@ cmd_shell() {
     fix_dir_perms $?
 }
 
+if [ $# = 0 ]; then
+    cmd_help
+    say_err "Please specify command to run!"
+    exit 1
+fi
+
 # Parse main command line args.
 #
 while [ $# -gt 0 ]; do