Integration using tools/datapath.go

- Instead of accessing `Endpoints` field directly on TestPartition, use
  GetEndpoints() function.
- refactor tools/datapath.go for meaningful log message.

Change-Id: I75fc2b3c7806fb0f40a1e7f324bc4b97fab05ac8
Reviewed-on: http://review.couchbase.org/38734
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>