add detection of duplicate ports to findPorts; fix smoke1 test

[mkinney]

Fix #270

[codecov]

Codecov Report

Merging #278 (e53a502) into master (ce8b75d) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #278      +/-   ##
==========================================
+ Coverage   89.14%   89.17%   +0.03%     
==========================================
  Files          13       13              
  Lines        2063     2060       -3     
==========================================
- Hits         1839     1837       -2     
+ Misses        224      223       -1     

Flag	Coverage Δ
unittests	89.17% <100.00%> (+0.03%)	⬆️

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Impacted Files	Coverage Δ
meshtastic/serial_interface.py	100.00% <100.00%> (+2.27%)	⬆️
meshtastic/util.py	75.50% <100.00%> (ø)

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