Update help text for hostnames

Change-Id: I9874f7f9e6d6d904aba3c5e639dd79908fe7ade8
Reviewed-on: http://review.couchbase.org/29172
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>