set $TARGET_MOUNT_POINT when running late-commands

so one does not have to pass --target to curtin in-target in a
late-command

subiquity/controllers/cmdlist.py

@@ -13,6 +13,8 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import os
+
 from subiquitycore.context import with_context
 from subiquitycore.utils import arun_command
 
@@ -35,14 +37,18 @@ class CmdListController(NoUIController):
     def load_autoinstall_data(self, data):
         self.cmds = data
 
+    def env(self):
+        return os.environ.copy()
+
     @with_context()
     async def run(self, context):
+        env = self.env()
         for i, cmd in enumerate(self.cmds):
             with context.child("command_{}".format(i), cmd):
                 if isinstance(cmd, str):
                     cmd = ['sh', '-c', cmd]
                 await arun_command(
-                    cmd,
+                    cmd, env=env,
                     stdin=None, stdout=None, stderr=None,
                     check=self.cmd_check)
 
@@ -56,6 +62,11 @@ class LateController(CmdListController):
 
     autoinstall_key = 'late-commands'
 
+    def env(self):
+        env = super().env()
+        env['TARGET_MOUNT_POINT'] = self.app.base_model.target
+        return env
+
     @with_context()
     async def apply_autoinstall_config(self, context):
         await self.run(context=context)