Authentication failure messages when bootstrap string includes non-kv nodes

When connection bootstrap string contains non-kv nodes, following error messages are seen:

2018-08-03 12:13:01 WARN  Endpoint:408 - [10.111.175.102:11210][KeyValueEndpoint]: Authentication Failure: Bucket not found on Select Bucket command
2018-08-03 12:13:01 DEBUG Node:191 - [10.111.175.102/10.111.175.102]: Disconnected (CONNECTING) from Node

These error messages are expected since memcached process on the non-kv nodes returns these errors when the client SDK connects to it for bootstrapping.  However, these Authentication errors can be misleading for the user and can make them concerned about the user credentials that are being used to connect to the Couchbase Cluster even though they may be accurate.

When non-kv nodes are a part of the bootstrap string, it will be useful if another user-friendly error message can be displayed to indicate the non-kv bootstrap use-case mentioned above for distinguishing between an actual error scenario and the bootstrap scenario.