Split test-submit-rule command into "test-submit rule"

Make "rule" a subcommand of the "test-submit" command.  This follows the
same pattern as the "plugin" set of commands and is a preparation for
introducing a command for testing submit type. The goal is to have a
dispatching "test-submit" command with "rule" and "type" as subcommands:

  test-submit rule ChangeId
  test-submit type ChangeId

Change-Id: I570a9e1931a257d9e64fd8b924e6d12f2d74d45d
1 file changed