Should allow graceful failover for query node without data service

If query will allow graceful failover we should allow CLI (and UI) to choose between graceful or hardfailover.

For example:

• setup 2 nodes cluster where 1 node is query ony
• perform failover of query node via couchbase-cli

# couchbase-cli failover -c localhost --username Administrator --password password --server-failover 172.23.120.102

ERROR: Failover cannot be done gracefully for a node without data service. Use hard failover. 

UI should also allow choice of graceful vs hard failover in the same case.