ejabberdctl: Detect problem running iex and show explanation

ejabberdctl.template

@@ -202,6 +202,24 @@ check_etop_result()
     fi
 }
 
+check_iex_result()
+{
+    result=$?
+    if [ $result -eq 127 ] ; then
+        echo ""
+        echo "It seems there was some problem finding 'iex' binary from Elixir."
+        echo "Probably ejabberd was compiled with Rebar3 and Elixir disabled, like:"
+        echo "  ./configure"
+        echo "which is equivalent to:"
+        echo "  ./configure --with-rebar=rebar3 --disable-elixir"
+        echo "To use 'iex', recompile ejabberd enabling Elixir or using Mix:"
+        echo "  ./configure --enable-elixir"
+        echo "  ./configure --with-rebar=mix"
+        echo ""
+        exit $result
+    fi
+}
+
 help()
 {
     echo ""
@@ -331,10 +349,12 @@ case $1 in
         debugwarning
         set_dist_client
         exec_iex "$(uid debug)" --remsh "$ERLANG_NODE"
+        check_iex_result
         ;;
     iexlive)
         livewarning
         exec_iex "$ERLANG_NODE" --erl "$EJABBERD_OPTS"
+        check_iex_result
         ;;
     ping)
         PEER=${2:-$ERLANG_NODE}