RF: Make archive (de)compression use WitlessRunner

[mih]

Another small step.

Went for a dedicated subshell to implement the pipe, rather than an exploration how to connect two runners. Not worse than what it was before.

[codecov]

Codecov Report

Merging #4900 into master will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4900      +/-   ##
==========================================
- Coverage   89.80%   89.76%   -0.04%     
==========================================
  Files         289      289              
  Lines       40659    40657       -2     
==========================================
- Hits        36512    36494      -18     
- Misses       4147     4163      +16     

Impacted Files	Coverage Δ
datalad/support/archive_utils_7z.py	90.90% <100.00%> (ø)
datalad/downloaders/http.py	81.85% <0.00%> (-2.71%)	⬇️
datalad/downloaders/tests/test_http.py	87.71% <0.00%> (-2.22%)	⬇️
datalad/utils.py	82.29% <0.00%> (-0.06%)	⬇️
datalad/core/distributed/push.py	89.11% <0.00%> (-0.05%)	⬇️
datalad/support/gitrepo.py	89.40% <0.00%> (-0.03%)	⬇️
datalad/support/annexrepo.py	89.00% <0.00%> (-0.01%)	⬇️
datalad/plugin/addurls.py	99.72% <0.00%> (-0.01%)	⬇️
datalad/tests/test_utils.py	96.15% <0.00%> (ø)
datalad/cmd.py	93.03% <0.00%> (+0.37%)	⬆️

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[kyleam]

Given that this function and the one below aren't returning the output, would it be better to use the KillOutput protocol?

[mih]

Oh. You are absolutely correct!

[mih]

Done

[mih]

Thanks for the review @kyleam. I made the switch to KillOutput and will merge now. All test failures are unrelated.

[bpoldrack]

Hm. test_archives just started failing in master in PY3.7: https://travis-ci.org/github/datalad/datalad/builds/725525494

I'm aware that it passed here, but since it only started now, seems related to this merge.