CCBC-185: Try to validate the bootstrap hosts

Change-Id: I13c4a16df29dce074ea7de60625e322ab17c3b40
Reviewed-on: http://review.couchbase.org/24619
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>