Fix issue with deletion of sessions during refresh()

[bworrell]

Description

Fixed an issue in TcpSessionHandler.refresh() where sessions may be skipped due to mutation of the list being iterated over.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

I added unit tests to confirm the undesired behavior and then implemented the fix (tests pass now).

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works

[bworrell]

Gonna update the test to not use IsolatedAsyncioTestCase since it was added in 3.8

[codecov]

Codecov Report

Merging #2055 (b1b1f80) into master (0cbac0c) will increase coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2055      +/-   ##
==========================================
+ Coverage   61.74%   61.87%   +0.13%     
==========================================
  Files          60       60              
  Lines        4243     4247       +4     
==========================================
+ Hits         2620     2628       +8     
+ Misses       1623     1619       -4     

Impacted Files	Coverage Δ
app/contacts/contact_tcp.py	47.82% <100.00%> (+6.91%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0cbac0c...b1b1f80. Read the comment docs.