Container: Start BEAM with exec to maintain the PID and catch SIGTERM in Docker Stop

Until now, when stopping the ejabberd container, Erlang is not gracefully
closed, Mnesia is not properly closed... exit code is 137.
With this change, when the container is stopped, Erlang receives the
SIGTERM signal, shutsdown, Mnesia database is properly closed, ...
and exit code is 0.

.github/container/ejabberdctl.template

@@ -109,13 +109,25 @@ export ERL_LIBS
 export SCRIPT_DIR
 
 # run command either directly or via su $INSTALLUSER
-exec_cmd()
+run_cmd()
 {
     case $EXEC_CMD in
         as_install_user) su -s /bin/sh -c '"$0" "$@"' "$INSTALLUSER" -- "$@" ;;
         as_current_user) "$@" ;;
     esac
 }
+exec_cmd()
+{
+    case $EXEC_CMD in
+        as_install_user) su -s /bin/sh -c '"$0" "$@"' "$INSTALLUSER" -- "$@" ;;
+        as_current_user) exec "$@" ;;
+    esac
+}
+run_erl()
+{
+    NODE=$1; shift
+    run_cmd "$ERL" ${S:--}name "$NODE" $ERLANG_OPTS "$@"
+}
 exec_erl()
 {
     NODE=$1; shift
@@ -253,7 +265,7 @@ wait_status()
         if [ $timeout -eq 0 ] ; then
             status="$1"
         else
-            exec_erl "$(uid ctl)" -hidden -noinput -s ejabberd_ctl \
+            run_erl "$(uid ctl)" -hidden -noinput -s ejabberd_ctl \
                      -extra "$ERLANG_NODE" $NO_TIMEOUT status > /dev/null
             status="$?"
         fi
@@ -262,7 +274,7 @@ wait_status()
 }
 
 # ensure we can change current directory to SPOOL_DIR
-[ -d "$SPOOL_DIR" ] || exec_cmd mkdir -p "$SPOOL_DIR"
+[ -d "$SPOOL_DIR" ] || run_cmd mkdir -p "$SPOOL_DIR"
 cd "$SPOOL_DIR" || {
     echo "ERROR: can not access directory $SPOOL_DIR"
     exit 6
@@ -317,7 +329,7 @@ case $1 in
         wait_status 3 30 2 && stop_epmd # wait 30x2s before timeout
         ;;
     *)
-        exec_erl "$(uid ctl)" -hidden -noinput -s ejabberd_ctl \
+        run_erl "$(uid ctl)" -hidden -noinput -s ejabberd_ctl \
                  -extra "$ERLANG_NODE" $NO_TIMEOUT "$@"
         result=$?
         case $result in