apply: Don't use staged deployments when /boot is automounted

The ostree staged deployment process works by waiting until shutdown to
swap the `/boot` symlinks to make the new deployment the default.
However, when `/boot` is the EFI System Partition and there's no `fstab`
entry, `systemd-gpt-auto-generator` sets up an automount so that the
VFAT filesystem is only exposed when needed.

Unfortunately, there are 2 bugs that make this process very fragile:

* Once a systemd automount unit is scheduled to be stopped, it ignores
  notifications from autofs that the target filesystem should be
  mounted. Therefore, if `/boot` isn't mounted when shutdown begins,
  `ostree admin finalize-staged` will fail. See
  systemd/systemd#22528.

* autofs is not mount namespace aware, so it will begin the expiration
  timer for a mount unit unless a process in the root namespace is
  keeping it active. Since `ostree admin finalize-staged` is run from a
  mount namespace (either via systemd or its own to ensure `/sysroot`
  and `/boot` are mounted read-write), the automount daemon (systemd)
  will try to unmount the filesystem if it expires during this process.
  See https://bugzilla.redhat.com/show_bug.cgi?id=2056090.

Therefore, if `/boot` is an autofs filesystem, use a full deployment
instead of a staged deployment. Since systems with an automounted
`/boot` are not common, we want to retain the benefit of staged
deployments for more normal systems. See
ostreedev/ostree#2543 for potential future
fixes in ostree.

https://phabricator.endlessm.com/T33136

eos-updater/apply.c

@@ -270,11 +270,13 @@ apply_internal (ApplyData     *apply_data,
 
   origin = ostree_sysroot_origin_new_from_refspec (sysroot, update_refspec);
 
-  /* When booted into an OSTree system, stage the deployment so that the
-   * /etc merge happens during shutdown. Otherwise (primarily the test
-   * suite), deploy the finalized tree immediately.
+  /* When booted into an OSTree system without an automount /boot, stage the
+   * deployment so that the /etc merge happens during shutdown. Otherwise
+   * (primarily sd-boot and the test suite), deploy the finalized tree
+   * immediately.
    */
-  staged_deploy = ostree_sysroot_is_booted (sysroot);
+  staged_deploy = ostree_sysroot_is_booted (sysroot) &&
+    !eos_updater_sysroot_boot_is_automount (sysroot, NULL);
   if (staged_deploy)
     {
       g_message ("Creating staged deployment for revision %s", update_id);