Use filelock in spawner to avoid concurrent operations

[saikishor]

Use filelock to avoid concurrent operations when launching more spawners at system startup and this should make it more robust.

I've tested spawning 30+ controllers with ros2_control_demos branch test/use/filelock/spawner, with this fix it works 10 out of 10 times and without this, it didn't even work once

Needs ros/rosdistro#45306

[doterkuile]

I have tested this PR on a robotic platform with 15 controllers spawning. The master version failed 20% of the times. With this PR there was 50/50 success rate.

[codecov]

Codecov Report

Attention: Patch coverage is 78.12500% with 7 lines in your changes missing coverage. Please review.

Project coverage is 89.09%. Comparing base (74cb0f0) to head (a169861).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
controller_manager/controller_manager/spawner.py	78.12%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2202      +/-   ##
==========================================
- Coverage   89.14%   89.09%   -0.05%     
==========================================
  Files         139      139              
  Lines       16124    16142      +18     
  Branches     1389     1390       +1     
==========================================
+ Hits        14373    14381       +8     
- Misses       1222     1229       +7     
- Partials      529      532       +3     

Flag	Coverage Δ
unittests	89.09% <78.12%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
controller_manager/controller_manager/spawner.py	73.54% <78.12%> (-0.91%)	⬇️

... and 1 file with indirect coverage changes

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[christophfroehlich]

LGTM

[bmagyar]

Thank you @saikishor and also @doterkuile for the notes on testing!