jp (application/list): don't use extend in argument as in it Python 3.8+ only

sat_frontends/jp/cmd_application.py

@@ -34,17 +34,26 @@ class List(base.CommandBase):
         )
 
     def add_parser_options(self):
+        # FIXME: "extend" would be better here, but it's only available from Python 3.8+
+        #   so we use "append" until minimum version of Python is raised.
         self.parser.add_argument(
             "-f",
-            "--filters",
-            action="extend",
-            nargs="+",
+            "--filter",
+            dest="filters",
+            action="append",
             choices=["available", "running"],
-            default=["available"],
             help=_("show applications with this status"),
         )
 
     async def start(self):
+
+        # FIXME: this is only needed because we can't use "extend" in
+        #   add_parser_options, see note there
+        if self.args.filters:
+            self.args.filters = list(set(self.args.filters))
+        else:
+            self.args.filters = ['available']
+
         try:
             found_apps = await self.host.bridge.applicationsList(self.args.filters)
         except Exception as e: