fix(controller): cast registrationEnabled to bool

etcd saves strings downcased. This changes the value from an
integer, which will be casted into a boolean.

fixes #992
Merge pull request #996 from deis/977-hotfix

fix(controller): cast registrationEnabled to bool
chore(contrib/*): update to CoreOS 317.0.0

Double-check the IDs:
EC2: https://coreos.com/docs/running-coreos/cloud-providers/ec2/
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