remove -J from test-ci and fix test-net-dns-custom-lookup

[rvagg]

This pulls in #1531 as well because it's the way to get passing builds on Jenkins when combined with removing -J from the test runner.

Ideally we should be able to use -J but it's borked on most of the build slaves but it would be nice if we could have it working so they are quicker to run. Something for @indutny to chime in on perhaps, @jbergstroem has also been looking at it.

Test run for these 2 commits: https://jenkins-iojs.nodesource.com/job/iojs+any-pr+multi/630/

[jbergstroem]

The rationale behind still using -J is that its faster (by running tests in parallel). If tests starts failing because of either higher load on the host or that the runner/jenkins or something else in the environment makes it fail that's something we need to fix. I'm afraid of ending up in a situation where we prefer sweeping things under the rug because we're gunning for test pass, no matter how we get there.

Anyway, -J was introduced with moving to make test-ci which is only a few days old. I'm happy to go back to our known state to ensure that 2.0 gets out but want to further investigate whats going on with our tests once run in parallel.

LGTM.

[rvagg]

yes, for the record, we haven't actually been using -J on CI until now but we should get there

[rvagg]

merged as 2a3c8c1, #1531 went in separately