Merge pull request #269 from spotify/rohan/fix-tests

Use docker-client 2.6.4
Break out TemporaryJobsTest into separate classes

We had a bunch of test classes stuffed into TemporaryJobsTest. Instead,
refactor the common functionality into TemporaryJobsTestBase and put each
class into its own file.

This also helps performance, since each separate test class can be run on
its own thread with forked execution.