mandos-ctl: Refactor

* mandos-ctl (TestBaseCommands): Rename test methods to match names of
                                 tested command.
  (TestBaseCommands.test_is_enabled): Rename to "test_IsEnabled".
  (TestBaseCommands.test_is_enabled_run_exits_successfully): Rename to
                              "test_IsEnabled_run_exits_successfully".
  (TestBaseCommands.test_is_enabled_run_exits_with_failure): Rename to
                              "test_IsEnabled_run_exits_with_failure".
  (TestBaseCommands.test_approve): Rename to "test_Approve".
  (TestBaseCommands.test_deny): Rename to "test_Deny".
  (TestBaseCommands.test_remove): Rename to "test_Remove".