[CDAP-900] [CDAP-1076] Changed the namespace create API to accept namespace-id as a PathParam. Added validations for namespace-id.
[CDAP-1076] Fixed broken unit tests
[CDAP-900] if reserved, throw a BAD_REQUEST instead of CONFLICT, since the CONFLICT can never be resolved.
Merge pull request #890 from caskdata/feature/CDAP-1076-create-namespace-api-update

[CDAP-900] [CDAP-1076] Changed the namespace create API to accept namesp...

Build passed - https://builds.cask.co/browse/CDAP-DUT395-3