COOPR-653: add partial templates REST API endpoints
COOPR-653: improve error message
Merge remote-tracking branch 'upstream/develop' into feature/coopr-653

Conflicts:
	coopr-server/src/main/java/co/cask/coopr/http/handler/AdminHandler.java
Merge remote-tracking branch 'upstream/develop' into feature/coopr-653
Addressed PR comments
Merge pull request #846 from cybervisiontech/feature/coopr-653

COOPR-653: Partial templates REST API endpoints