Replace deprecated threading.currentThread

[BrianJKoopman]

Description

See deprecation note in the threading docs: https://docs.python.org/3/library/threading.html#threading.current_thread

Motivation and Context

This shows up when running tests:

  /home/koopman/git/ocs/ocs/ocs_twisted.py:129: DeprecationWarning: currentThread() is deprecated, use current_thread() instead
    t = threading.currentThread()

How Has This Been Tested?

Tests run locally.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.