Switch to a more reliable way of discovering when the environment
information is available.
Merge pull request #808 from ClusterHQ/intermittent-test-failure-806

Switch to a more reliable testing method.

Fixes #806.
Merge remote-tracking branch 'refs/remotes/origin/master' into volume-namespaces-771

Conflicts:
	flocker/node/functional/test_deploy.py
Lint fix.