wayland: Drop -terminate argument to Xwayland

This argument instructs Xwayland to exit when there are no further
client connections. However we eventually want to handle restarts
ourselves (where, notably, mutter's will be at least the last client
connection).

This behavior could also induce race conditions on startup with clients
that quickly open and close a display, which is a more pressing issue.

Also, add -noreset back (which was also removed in commit 054c25f693 that
added -terminate). We don't want to reset the X server to a pristine state
in that situation either.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/420

src/wayland/meta-xwayland.c

@@ -506,16 +506,10 @@ meta_xwayland_init_xserver (MetaXWaylandManager *manager)
 
   g_subprocess_launcher_setenv (launcher, "WAYLAND_SOCKET", "3", TRUE);
 
-  /* Use the -terminate parameter to ensure that Xwayland exits cleanly
-   * after the last client disconnects. Fortunately that includes the window
-   * manager so it won't exit prematurely either. This ensures that Xwayland
-   * won't try to reconnect and crash, leaving uninteresting core dumps. We do
-   * want core dumps from Xwayland but only if a real bug occurs...
-   */
   manager->proc = g_subprocess_launcher_spawn (launcher, &error,
                                                XWAYLAND_PATH, manager->display_name,
                                                "-rootless",
-                                               "-terminate",
+                                               "-noreset",
                                                "-accessx",
                                                "-core",
                                                "-listen", "4",