Refactor before fixing support for re-attach.

[ericsnowcurrently]

An alternative approach to fixing re-attach (in contrast to #287) requires separating some concerns that are currently mixed together in the code base. This PR does so.

[codecov-io]

Codecov Report

Merging #296 into master will increase coverage by 1.33%.
The diff coverage is 72.24%.

@@           Coverage Diff            @@
##           master   #296      +/-   ##
========================================
+ Coverage   62.66%    64%   +1.33%     
========================================
  Files          11     14       +3     
  Lines        1875   1989     +114     
========================================
+ Hits         1175   1273      +98     
- Misses        700    716      +16

Impacted Files	Coverage Δ
ptvsd/__main__.py	91.54% <100%> (ø)	⬆️
ptvsd/pydevd_hooks.py	61.29% <61.29%> (ø)
ptvsd/daemon.py	67.22% <67.22%> (ø)
ptvsd/wrapper.py	50.47% <78.57%> (+0.18%)	⬆️
ptvsd/socket.py	90.32% <90.32%> (ø)
ptvsd/ipcjson.py	66.82% <0%> (+1.46%)	⬆️

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[int19h]

I really like this code reorganization, much neater compared to our existing everything-in-wrapper.py! 👍

[DonJayamanne]

Running PTVSD fails (error message attached)

[DonJayamanne]

@ericsnowcurrently
This PR breaks debugging using launch as well as attach.
Looks like we need some better unit tests. #292 is another example where we need unit tests for a similar if not exact scenario. I've attempted to fix the issue without any tests.

[DonJayamanne]

I really like this code reorganization, much neater compared to our existing everything-in-wrapper.py! 👍

Agreed.

[ericsnowcurrently]

@DonJayamanne This PR should no longer break debugging. Please verify. As to the tests, I agree and am working on it. :)