don't reload pool details if etag is missing

Change-Id: I89c4d22614c6419074c88e7a82bcc5a1f824fc9c
Reviewed-on: http://review.couchbase.org/35887
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>