Add unistd.h to header.
Add unistd.h to header.

Includes a different and this is causing a build break on centos 7.

Change-Id: I71a6760ce99faf9b93bfa16a3c7135b88018bab3
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/6842
Reviewed-by: Chao Sun <67a7c7fa38d7a5d78492d6f0626602205a411205@cloudera.com>
Tested-by: jenkins

cloudera/RecordServiceClient,cloudera/RecordServiceClient,cloudera/RecordServiceClient,cloudera/RecordServiceClient,cloudera/RecordServiceClient