[#615] Add support to reset current process effective user

[adiroiban]

Scope

Fixes #615

This is a hack to somehow fix a threading issue that we have in chevah/server

Our whole code is not designed for running threads with separate user context.

This is a fix only for Linux... but out customer that use this only use Linux.

Changes

Add support for run in non-blocking mode... so if an I/O operation is blocked, the whole process is not.

Add some unit tests

How to try and test the changes

reviewers: @dumol

More of a FYI

The actual testing should be done in chevah/server

The main tests are at https://github.com/chevah/server/pull/6975

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.74%. Comparing base (d8847a8) to head (85c2c7c).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #715      +/-   ##
==========================================
- Coverage   78.93%   78.74%   -0.19%     
==========================================
  Files          50       50              
  Lines        7828     7895      +67     
  Branches      635      634       -1     
==========================================
+ Hits         6179     6217      +38     
- Misses       1377     1416      +39     
+ Partials      272      262      -10     

see 11 files with indirect coverage changes

Components	Coverage Δ
tests	∅ <ø> (∅)

[adiroiban]

needs-review

[dumol]

More of a FYI

ACK. Tests passed.

changes-approved