Merge pull request #2158 from bowlofeggs/su-with-sh

Use /bin/sh as the explicit shell when using su in ejabberdctl.

ejabberdctl.template

@@ -110,7 +110,7 @@ export ERL_LIBS
 exec_cmd()
 {
     case $EXEC_CMD in
-        as_install_user) su -c '"$0" "$@"' "$INSTALLUSER" -- "$@" ;;
+        as_install_user) su -s /bin/sh -c '"$0" "$@"' "$INSTALLUSER" -- "$@" ;;
         as_current_user) "$@" ;;
     esac
 }