testing: metrics_delta.py fixes

[brianolson]

Summary

Fixes found during recent cluster bandwidth testing

Test Plan

This is test code for manual tests.

[codecov-commenter]

Codecov Report

Merging #2962 (dd91b9d) into master (073717e) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2962      +/-   ##
==========================================
- Coverage   47.57%   47.56%   -0.01%     
==========================================
  Files         358      358              
  Lines       57863    57863              
==========================================
- Hits        27527    27524       -3     
- Misses      27211    27216       +5     
+ Partials     3125     3123       -2     

Impacted Files	Coverage Δ
catchup/service.go	68.57% <0.00%> (-1.56%)	⬇️
network/wsNetwork.go	60.90% <0.00%> (-0.19%)	⬇️
ledger/acctupdates.go	62.58% <0.00%> (+0.08%)	⬆️
ledger/blockqueue.go	82.18% <0.00%> (+1.14%)	⬆️
cmd/algoh/blockWatcher.go	80.95% <0.00%> (+3.17%)	⬆️

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[tsachiherman]

Please rerun failed tests

[algobolson]

filed issue for flakey test. re-run started.