Fix #37, Add cancellation point to idle task

[skliper]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fix HS_IdleTask has no cancellation point #37

Just adds cancellation point to the idle task

Testing performed
CI, and confirmed cFS exits cleanly with Ctrl-C

Expected behavior changes
HS idle task now exits cleanly

System(s) tested on
CI and Linux

Additional context
None

Third party code
None

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

@excaliburtb