tests: fix debug output in expect test harness

[algorandskiy]

Summary

The original implementation had scoping issue with tcp_platform global var as this build indicated.
Additionally added stdout redirect for exec since its behavior in a script differs from REPL where I tested the original code.

Test Plan

This is a test harness change.

[codecov]

Codecov Report

Merging #5158 (81fa781) into master (8bb071f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5158   +/-   ##
=======================================
  Coverage   53.57%   53.57%           
=======================================
  Files         434      434           
  Lines       54748    54748           
=======================================
  Hits        29333    29333           
- Misses      23131    23133    +2     
+ Partials     2284     2282    -2     

Impacted Files	Coverage Δ
ledger/tracker.go	72.91% <0.00%> (-3.75%)	⬇️
ledger/acctupdates.go	68.53% <0.00%> (-0.48%)	⬇️
catchup/service.go	70.82% <0.00%> (-0.24%)	⬇️
network/wsNetwork.go	69.14% <0.00%> (-0.18%)	⬇️
ledger/testing/randomAccounts.go	56.26% <0.00%> (ø)
network/wsPeer.go	71.95% <0.00%> (+2.52%)	⬆️
ledger/blockqueue.go	84.94% <0.00%> (+2.68%)	⬆️

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[bbroder-algo]

yup

[algonautshant]

Looks fine.