Describe the contribution

• Turned all FIXME comments into issues (and removed FIXME)
• Fix lgtm issues for os-impl-posix-files.c, osapi-filesys.c #333: security/filename race issue resolved by opening file and acting on descriptor (had to add fstat stub)
• Fix Recommended lgtm osal issues #327: squashed the minor recommended bugs

Testing performed
Built and ran unit tests, passed.

Expected behavior changes
None

System(s) tested on

• Hardware: cFS Dev Server
• OS: Ubuntu 18.04
• Versions: bundle main + this commit

Additional context
#630, #632 - new issues from FIXME
#631 - uncovered missing functional test on OS_chmod

Third party code
None

Contributor Info - All information REQUIRED for consideration of pull request
Jacob Hageman - NASA/GSFC