build: use synth templates and kokoro config

[kjin]

This PR brings in a workable kokoro configuration. However, code coverage reporting remains TBD.

Note that on Windows, integration (plugin) tests are not run.

Dependent on #1059, #1060, #1061; only the first two commits in this PR are unique; the rest will be erased once these PRs land.

This is meant to supersede #1049, but I'm not sure if it checks all the boxes listed there.

[kjin]

cc/ @JustinBeckwith

[codecov]

Codecov Report

Merging #1062 into master will decrease coverage by 3.18%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1062      +/-   ##
==========================================
- Coverage   94.86%   91.68%   -3.19%     
==========================================
  Files          96      114      +18     
  Lines        6327     6611     +284     
  Branches      496      496              
==========================================
+ Hits         6002     6061      +59     
- Misses        166      391     +225     
  Partials      159      159

Impacted Files	Coverage Δ
.jsdoc.js	0% <0%> (ø)
test/plugins/test-trace-http.ts	100% <0%> (ø)	⬆️
...t/fixtures/source-maps-test/external-source-map.js	0% <0%> (ø)
test/non-interference/express-e2e.js	0% <0%> (ø)
system-test/trace-express.js	0% <0%> (ø)
samples/app.js	0% <0%> (ø)
...est/fixtures/source-maps-test/inline-source-map.js	0% <0%> (ø)
...est/fixtures/source-maps-test/inline-source-map.ts	0% <0%> (ø)
samples/snippets.js	0% <0%> (ø)
... and 22 more

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[bcoe]

this looks like a slightly older version of config then is currently live in synthtool. We dropped -xeo and went with -eo, because -x leaks a lot of environment information.

[kjin]

I see. I used the stable build of synthtool. Sure enough with latest the contents have now changed.

[bcoe]

I'll see about getting a new version of synthtool out the door.

[kjin]

Note -- I would like to get coverage working before merging this.

[kjin]

OK, I've fixed coverage. (For posterity, .nycrc needs to be ignored for now, as the Trace Agent has a script for producing per-test-file coverage rather than test-suite-wide coverage.)