filesystem: fix failed zpool export

Ordering matters of zpool export, or we get an 'export failed' error.
If one does a force reboot the export was not performed, and we
initramfs-prompt until someone does `zpool import -f $poolname`.

subiquity/models/filesystem.py

@@ -1095,9 +1095,6 @@ class ZPool:
     def mount(self):
         return self.mountpoint
 
-    async def pre_shutdown(self, command_runner):
-        await command_runner.run(['zpool', 'export', self.pool])
-
 
 @fsobj("zfs")
 class ZFS:

subiquity/server/controllers/filesystem.py

@@ -1329,5 +1329,5 @@ class FilesystemController(SubiquityController, FilesystemManipulator):
         if not self.reset_partition_only:
             await self.app.command_runner.run(
                 ['umount', '--recursive', '/target'])
-        for pool in self.model._all(type='zpool'):
-            await pool.pre_shutdown(self.app.command_runner)
+        if len(self.model._all(type='zpool')) > 0:
+            await self.app.command_runner.run(['zpool', 'export', '-a'])