rescue: Don't allow to mount systems without a root device

If the rescue mode founds an operating system with /etc/fstab without the root
device (because it is, for example, commented out), it should ignore this system
instead of trying to mount it. If there are no Linux systems to mount, show the
"No Linux systems found" message instead of "You don't have any Linux partitions".

(cherry-picked from a commit c440e7c)

Related: RHEL-14696

pyanaconda/rescue.py

@@ -174,13 +174,18 @@ def find_roots(self):
         task_proxy = STORAGE.get_proxy(task_path)
         sync_run_task(task_proxy)
 
+        # Collect existing systems.
         roots = OSData.from_structure_list(
             self._device_tree_proxy.GetExistingSystems()
         )
 
+        # Ignore systems without a root device.
+        roots = [r for r in roots if r.get_root_device()]
+
         if not roots:
             self.status = RescueModeStatus.ROOT_NOT_FOUND
 
+        log.debug("These systems were found: %s", str(roots))
         return roots
 
     # TODO separate running post scripts?
@@ -451,7 +456,7 @@ def refresh(self, args=None):
                     finish_msg = exit_reboot_msg
                 else:
                     finish_msg = ""
-                text = TextWidget(_("You don't have any Linux partitions.\n") + finish_msg)
+                text = TextWidget(_("No Linux systems found.\n") + finish_msg)
         else:
             if self._rescue.reboot:
                 finish_msg = exit_reboot_msg