Nifi Couchbase Processors does not support User Authentication

Issue Description: Nifi Couchbase processors don't work with new couchbase versions 5.0 and 5.1.

New Couchbase Version 5.x has introduced Role Based Access Control (RBAC), a ** new security feature.

1. All buckets must now be accessed by a user/password combination that has a role with access rights to the bucket.
2. Buckets no longer use bucket-level passwords
3. There is no default bucket and no sample buckets with blank passwords.
4. You cannot create a user without a password.

(Ref: https://developer.couchbase.com/documentation/server/5.0/introduction/whats-new.html

https://blog.couchbase.com/new-sdk-authentication/ )

nifi-couchbase-processors : GetCouchbaseKey and PutCouchbaseKey using Controller Service still uses old authentication mechanism.

• org.apache.nifi.processors.couchbase.GetCouchbaseKey
• org.apache.nifi.processors.couchbase.PutCouchbaseKey

Ref: https://github.com/apache/nifi/blob/master/nifi-nar-bundles/nifi-couchbase-bundle/nifi-couchbase-processors/src/main/java/org/apache/nifi/couchbase/CouchbaseClusterService.java#L116