Add err to test.retryErr list if retrying the test #2529

[LToronto]

Adds the ability to see the errors from earlier attempts. Occasional
the test state is different during the retry and the last test error is
not helpful. Is this case the first error (test.retryErr[0]) is
useful.

[jsf-clabot]

All committers have signed the CLA.

[coveralls]

Coverage increased (+0.01%) to 88.405% when pulling 033dd02 on LToronto:retryErr into 1f270cd on mochajs:master.

[coveralls]

Coverage increased (+0.01%) to 88.405% when pulling 4e62523 on LToronto:retryErr into 1f270cd on mochajs:master.

[LToronto]

It looks like node version 0.10 is broken in master. There's nothing I should do here to fix it.

[ScottFreeCode]

Hi @LToronto, thanks for the PR! And sorry about the delay responding to it.

One question I have about this is whether it would suffice to emit an event when a test is retried, that would contain the failure info such that you could save it if you want to or print it at the time it happens (rather than having to wait until the last test attempt ends to get the list of retried failures). While that's a little more work on the part of the consumer of that info, I believe it serves a superset of the use cases of this approach; I've also discussed that aspect in #2529 (comment) and that other approach should be implemented by #2926 if you want to check it out and try it.

(By the way, the Node 0.10 failure should be fixed in master now if you want to rebase -- or add tests.)

[LToronto]

Closed in favor of #2926