Stylistic fixes after review 'separate provisioning/deployment' feature

* empty line between build-in and third party modeuls in import
* simpler validator selection

Implements: blueprint nailgun-separate-provisioning-and-deployment-handlers
Change-Id: I6c39a2ec7d304dd32ba8d3964c0d110fc17f3016
Merge "Stylistic fixes after review 'separate provisioning/deployment' feature"