External Data Source: Set scan handle parameter in close()

Change-Id: Ibd2d61ba52a4532b0f7b79224f70abbff1b363e4
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2519
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: jenkins
Enforce slot equivalences at data source scan nodes

Change-Id: I2ed606ba398990ab05afa3301b6356c6a636e2bb
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2521
Reviewed-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: jenkins