MILC: Use dashes instead of underscores for subcommands

The subcommand functions' name follows the Python convention of using
snake case, but looks odd on the command line.
Fix it by converting underscores to dashes, eg.: list_keyboards ->
list-keyboards.

lib/python/qmk/tests/test_cli_commands.py

@@ -40,7 +40,7 @@ def test_pyformat():
 
 
 def test_list_keyboards():
-    result = check_subcommand('list_keyboards')
+    result = check_subcommand('list-keyboards')
     assert result.returncode == 0
     # check to see if a known keyboard is returned
     # this will fail if handwired/onekey/pytest is removed