[RFC] Improved Subtest-bypass control about autotest-docker

[cevich]

dang, in fact, we can't have control write config_custom/control.ini because test-skipping needs to happen via exclusion from the steps engine. So it really does all have to happen inside the control file, and not interact with subtest config at all 😖

[cevich]

To address #114, one idea might be to use a special character like "~" to invert meaning of --args. i.e. skip the listed tests instead of run only listed tests.

[cevich]

This issue has been resolved by extending --args processing to include two new tokens: 'i=' and 'x=' to specify specific sub/sub-subtests to include or xclude. This was really difficult to pull off and required extending not only the control file but many aspects of the Subtest, SubSubtest, and SubSubtestCaller classes. One nice side-effect is that it's now possible for SubSubtestCaller's to dynamically generate their own subsubtests at module-load time. All of this is in #109