Pin pywin32 dependency

[ofek]

Motivation

Move toward defining all requirements in -core itself rather than the build system

[codecov-io]

Codecov Report

Merging #2322 into master will decrease coverage by 23.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2322      +/-   ##
==========================================
- Coverage   85.87%   62.77%   -23.1%     
==========================================
  Files         192       42     -150     
  Lines       13463     2598   -10865     
  Branches     1452      442    -1010     
==========================================
- Hits        11561     1631    -9930     
+ Misses       1487      836     -651     
+ Partials      415      131     -284

[gmmeyer]

have you tested the build yet? does it work? we need to do that before we merge this

[ofek]

I did test windows service and sqlserver manually using the new builds, not the others. Though if those work I'm not sure how I could test the others in such a way that would expose anything the tests haven't.

Also, I still need to actually remove the omnibus dep definition after this is merged.