Use click.Group instead of MultiCommand

MultiCommand has been deprecated and it is now an alias to Group,
which leads to new mypy warnings when running mypy with Click
available in the environment.

Author: ldionne

lnt/lnttool/admin.py

@@ -341,7 +341,7 @@ def action_create_config():
     sys.stderr.write("Created '%s'\n" % _default_config_filename)
 
 
-class AdminCLI(click.MultiCommand):
+class AdminCLI(click.Group):
     '''Admin subcommands. Put into this class so we can lazily import
     dependencies.'''
     _commands = [

lnt/lnttool/main.py

@@ -142,7 +142,7 @@ def _print_result_url(results, verbose):
         print("Results available at: no URL available")
 
 
-class RunTestCLI(click.MultiCommand):
+class RunTestCLI(click.Group):
     def list_commands(self, ctx):
         import lnt.tests
         return lnt.tests.get_names()