all: Switch the --lang syntax to use argv instead

It was a bit awkward using `mgmt run lang --lang <input>` so instead, we
now drop the --lang, and read the positional argv for the input.

This also does the same for the --yaml frontend.

test/shell/exec-usergroup.sh

@@ -40,7 +40,7 @@ function run_usergroup_test() {
 	setup
 
 	# run till completion
-	sudo -A $TIMEOUT "$MGMT" run --converged-timeout=15 --no-watch --tmp-prefix yaml --yaml ./exec-usergroup/${graph} &
+	sudo -A $TIMEOUT "$MGMT" run --converged-timeout=15 --no-watch --tmp-prefix yaml ./exec-usergroup/${graph} &
 	pid=$!
 	wait $pid	# get exit status
 	e=$?