Fixed directory creation to ignore umask, and allow cross process loc…

[JonathanHenson]

…k to fall back to read only if it can't open the file in rw mode.

testing on this one is hard to automate. Here's how I verified:

create lock directory as user, create lock as user, make sure it works
create lock dir as user, create lock as root, make sure it works for user
create lock dir as root, create lock as root, make sure it works for user
create lock dir as root, try to create lock as user, make sure it works for user.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[nateprewitt]

LGTM after tests wrap

[codecov-commenter]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (fefbf4b) 83.40% compared to head (c137a09) 83.30%.

Files	Patch %	Lines
source/posix/cross_process_lock.c	26.66%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1078      +/-   ##
==========================================
- Coverage   83.40%   83.30%   -0.11%     
==========================================
  Files          56       56              
  Lines        5792     5804      +12     
==========================================
+ Hits         4831     4835       +4     
- Misses        961      969       +8     

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