Feature/spawn with interfacer

[shuds13]

This branch makes the Optimas/APOSMM example work with spawn, as well as fork.

I have removed the extra comm created with the multiprocessing server queues and instead am using the QCommProcess
directly. I have not tried with a thread as yet, but it works with a process.

Spawn still failed due to a threadlock on the executor comm attribute (which is added in worker.py). This would be the wrong comm anyway when passing to the APOSMM process. Removing this enables spawn to work.

Some attention needs to be paid to passing the executor, to ensure this works both when actually used in the gen and when no executor exists.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 78.76%. Comparing base (043feeb) to head (c323ef8).
Report is 146 commits behind head on experimental/jlnav_plus_shuds_asktell.

Files with missing lines	Patch %	Lines
libensemble/generators.py	77.77%	1 Missing and 1 partial ⚠️

❗ There is a different number of reports uploaded between BASE (043feeb) and HEAD (c323ef8). Click for more details.

HEAD has 14 uploads less than BASE

Flag	BASE (043feeb)	HEAD (c323ef8)
	24	10

Additional details and impacted files

@@                            Coverage Diff                             @@
##           experimental/jlnav_plus_shuds_asktell    #1464       +/-   ##
==========================================================================
- Coverage                                  90.93%   78.76%   -12.17%     
==========================================================================
  Files                                         80       81        +1     
  Lines                                       8086     8072       -14     
  Branches                                    1434     1196      -238     
==========================================================================
- Hits                                        7353     6358      -995     
- Misses                                       555     1504      +949     
- Partials                                     178      210       +32     

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