[test-framework] Cleaning up test application

[nmittler]

This is in preparation for migrating all Istio tests to use this
application.

[nmittler]

@ozevren this is factored out of #9381 to simplify review and submission

[codecov]

Codecov Report

Merging #9413 into master will increase coverage by 1%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #9413    +/-   ##
=======================================
+ Coverage      70%     70%    +1%     
=======================================
  Files         424     423     -1     
  Lines       39333   39258    -75     
=======================================
+ Hits        27333   27452   +119     
+ Misses      10701   10509   -192     
+ Partials     1299    1297     -2

Impacted Files	Coverage Δ
mixer/adapter/signalfx/tracing.go	80% <0%> (-4%)	⬇️
mixer/adapter/servicecontrol/reportprocessor.go	79% <0%> (-1%)	⬇️
mixer/adapter/statsd/statsd.go	96% <0%> (-1%)	⬇️
pilot/pkg/model/validation.go	82% <0%> (ø)	⬇️
mixer/pkg/protobuf/yaml/wire/wire.go	98% <0%> (ø)	⬇️
mixer/adapter/circonus/circonus.go	71% <0%> (ø)	⬇️
mixer/template/template.gen.go	0% <0%> (ø)	⬆️
mixer/adapter/list/regexList.go	100% <0%> (ø)	⬆️
mixer/adapter/memquota/memquota.go	100% <0%> (ø)	⬆️
mixer/adapter/memquota/keys.go	100% <0%> (ø)	⬆️
... and 12 more

---

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[ozevren]

/lgtm
/approve

[istio-testing]

[APPROVALNOTIFIER] This PR is APPROVED

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This pull-request has been approved by: ozevren

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• tests/OWNERS

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[nmittler]

/test e2e-simpleTests

[nmittler]

/test istio-unit-tests

[istio-testing]

@nmittler: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
prow/e2e-mixer-no_auth-mcp.sh	035b726	link	/test e2e-mixer-no_auth-mcp

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