WIP: testcase discovery split, #1

adds all the engines in tcfl.testcase, tcfl.tc_c to be able to
discover a new style testcase.

Still fails, but handles the failure and reports about it.

Moves a lot of code from tcfl.tc.py to:

- tcfl/testcase.py: internal handling of discovery, etc

- tcfl/__init__.py: pure testcase execution

- tcfl/ui_cli_testcase.py: command line interface to testcase discovery

Removes:

- extra_report_format: unused

- runid_visible: replace with plain runid

tcf

@@ -504,8 +504,8 @@ if __name__ == "__main__":
  # line interface
  import tcfl.target_ext_alloc_ui
  tcfl.target_ext_alloc_ui._cmdline_setup(arg_subparsers)
- import tcfl.ui_cli_run
- tcfl.ui_cli_run._cmdline_setup(arg_subparsers)
+ import tcfl.ui_cli_testcases
+ tcfl.ui_cli_testcases._cmdline_setup(arg_subparsers)
 
  ap = arg_subparsers.add_parser("healthcheck",
  help = "Do a very basic health check")