build dask-kubernetes from master

[delgadom]

Workflow

• [x] Closes issue #72
• [ ] Notebook:worker pairing builds & passes local build, visual inspection & client.map tests
• [x] Passes travis tests
• [ ] Image deployed on dev branch (see notebook and worker dev tags)
• [ ] Worker passes manual deployment test on compute.rhg
• [x] Notebook+worker passes test-hub deployment
• [x] Updates integrated into downstream images

Summary

Pulls dask-kubernetes from master (pinned to commit 295f064). This is an attempt to fix the autoscaling & scale down issue.