chore(run): Pass through to subprocess.Popen

[tony]

As part of us migrating to SubprocessCommand #340 , make existing run() directly compatible with subprocess.Popen

[codecov]

Codecov Report

Merging #361 (b4b7a5d) into master (b7bde3b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #361   +/-   ##
=======================================
  Coverage   70.22%   70.22%           
=======================================
  Files          21       21           
  Lines        1857     1857           
=======================================
  Hits         1304     1304           
  Misses        553      553           

Impacted Files	Coverage Δ
libvcs/cmd/git.py	54.16% <100.00%> (ø)
libvcs/cmd/hg.py	69.73% <100.00%> (ø)
libvcs/cmd/svn.py	52.23% <100.00%> (ø)

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