ci: Reduce log output in test_cover

[ValarDragon]

This commit makes it such that circle CI only shows the module whose
tests it is currently running in the log, unless a test fails. For each
failing test, it will display the name of all failing tests, along with
their log output. This is done to make
our log output far more scrollable. We lose no information in debugging.

An example with go test:
I added t.Log("test name") and t.Fail() to the bottom of two tests, and then ran go test, the following log output appeared:

 go test
--- FAIL: TestErrorPanic (0.00s)
	errors_test.go:30: TESTERRORPANIC
--- FAIL: TestErrorNewErrorWithTrace (0.00s)
	errors_test.go:97: TestErrorNewErrorWithTrace

(This test code is not in the commit, its just meant to show how it works)
Take a look at the CI logs!

• Updated all relevant documentation in docs - n/a
• Updated all code comments where relevant - n/a
• Wrote tests - n/a
• Updated CHANGELOG.md - not user facing, only affects CI + reviewing PR's

[codecov-io]

Codecov Report

Merging #2105 into develop will decrease coverage by 0.31%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #2105      +/-   ##
===========================================
- Coverage    62.73%   62.42%   -0.32%     
===========================================
  Files          215      215              
  Lines        17376    17369       -7     
===========================================
- Hits         10901    10842      -59     
- Misses        5586     5637      +51     
- Partials       889      890       +1

Impacted Files	Coverage Δ
p2p/pex/errors.go	0% <0%> (-20%)	⬇️
p2p/node_info.go	45.61% <0%> (-5.27%)	⬇️
consensus/reactor.go	73.02% <0%> (-4.84%)	⬇️
proxy/client.go	22.22% <0%> (-3.59%)	⬇️
libs/common/os.go	16.9% <0%> (-3.1%)	⬇️
mempool/reactor.go	64.19% <0%> (-2.47%)	⬇️
p2p/peer.go	57.95% <0%> (-2.28%)	⬇️
evidence/reactor.go	65.93% <0%> (-2.2%)	⬇️
p2p/pex/pex_reactor.go	71.86% <0%> (-1.7%)	⬇️
p2p/listener.go	49.59% <0%> (-1.63%)	⬇️
... and 6 more

[xla]

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