Update token endpoint + fix failing tests

[ace-n]

When I try to use this library in an npm Container Builder step (via the Cloud Storage API), I get the following error:

{ Error: 404 page not found
at new RequestError (/workspace/functions/autodeploy/node_modules/google-auth-library/lib/transporters.js:34:42)
at Request._callback (/workspace/functions/autodeploy/node_modules/google-auth-library/lib/transporters.js:108:23)
at Request.self.callback (/workspace/functions/autodeploy/node_modules/request/request.js:186:22)
at emitTwo (events.js:126:13)
at Request.emit (events.js:214:7)
at Request.<anonymous> (/workspace/functions/autodeploy/node_modules/request/request.js:1163:10)
at emitOne (events.js:116:13)
at Request.emit (events.js:211:7)
at IncomingMessage.<anonymous> (/workspace/functions/autodeploy/node_modules/request/request.js:1085:12)
at Object.onceWrapper (events.js:313:30)
at emitNone (events.js:111:20)
at IncomingMessage.emit (events.js:208:7)
at endReadableNT (_stream_readable.js:1056:12)
at _combinedTickCallback (internal/process/next_tick.js:138:11)
at process._tickCallback (internal/process/next_tick.js:180:9) code: 404 }

To (potentially) fix this, I've changed the v1beta1 token endpoint URL to use v1, which in my tests returned a token (as opposed to 404ing like the v1beta1 URL).

I've also updated the tests accordingly, and added timeouts to a few unrelated-but-flaky tests to ensure that they pass.

[codecov-io]

Codecov Report

Merging #269 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #269   +/-   ##
=======================================
  Coverage   93.91%   93.91%           
=======================================
  Files          13       13           
  Lines         838      838           
  Branches      182      182           
=======================================
  Hits          787      787           
  Misses         51       51

Impacted Files	Coverage Δ
src/auth/computeclient.ts	94.73% <ø> (ø)	⬆️

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