Refactor: cts,python: Consolidate add_cmd methods into the Test module.

• Move the generic versions of these functions in cts-fencing.in into the Test module.

• Add add_cmd_and_kill from cts-exec.in to the Test module as well, since it seems like it might be more broadly useful. Reorder its parameters to match other methods.

• Rename add_expected_fail_cmd to add_cmd_expected_fail to match how other methods are named.

• Since the cmd is always self._test_tool_location in cts-exec.in, keep the more specific versions of these methods that then call into the Test module versions.