Hardening patchset

[ChrisCummins]

This patch set contains a handful of fixes for issues discovered while trying to track down #572:

• Corrects a misuse of the boost::process API, fixing a bug wherein llvm-size child processes could become detached from the parent environment service and be left as zombie processes.
• Disables TCP port reuse for all gRPC channels, as it has been reported to occasionally interfere with port autoselect (see Server port autoselect doesn't work reliably with SO_REUSEPORT on. grpc/grpc#10755).
• Ensures that all gRPC client/server connection options in both Python and C++ use the same configuration options.
• Fix a bug in which connection liveness was reported exactly the wrong way around (dead services were logged as alive and alive connections as dead).
• Replaces get_system_includes() with get_system_library_flags(), a function that returns a list of -isystem flags, and a -L flag for macOS. This enables optimizing for runtime on macOS.
• Holds the gRPC version back below 1.44 until I can diagnose the new error messages raised in the new version. See E0216 from backup_poller.cc or ev_epollex_linux.cc #572.
• Adds a 300 second timeout to all tests when using the pytest test runner.

[mostafaelhoushi]

LGTM

[codecov-commenter]

Codecov Report

Merging #578 (25c982d) into development (1d095e2) will increase coverage by 0.18%.
The diff coverage is 97.43%.

@@               Coverage Diff               @@
##           development     #578      +/-   ##
===============================================
+ Coverage        88.09%   88.27%   +0.18%     
===============================================
  Files              114      114              
  Lines             6693     6705      +12     
===============================================
+ Hits              5896     5919      +23     
+ Misses             797      786      -11     

Impacted Files	Coverage Δ
compiler_gym/envs/compiler_env.py	89.77% <ø> (-1.75%)	⬇️
compiler_gym/envs/llvm/__init__.py	100.00% <ø> (ø)
compiler_gym/envs/llvm/llvm_env.py	87.27% <ø> (ø)
compiler_gym/service/connection.py	82.95% <75.00%> (+6.96%)	⬆️
compiler_gym/envs/llvm/datasets/cbench.py	80.74% <100.00%> (+0.07%)	⬆️
compiler_gym/envs/llvm/datasets/csmith.py	86.84% <100.00%> (+0.17%)	⬆️
compiler_gym/envs/llvm/llvm_benchmark.py	93.43% <100.00%> (+2.73%)	⬆️
...ice/runtime/create_and_run_compiler_gym_service.py	100.00% <100.00%> (ø)
compiler_gym/views/observation_space_spec.py	85.71% <0.00%> (-3.58%)	⬇️
...loop_tool/service/loop_tool_compilation_session.py	88.43% <0.00%> (-2.73%)	⬇️
... and 5 more

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