IMPALA-1028: Cardinality estimate is wrong for partitioned tables if we
filter out all partitions

This commit fixes IMPALA-1028 in which the cardinality estimate is not
correct when all the partitions of a partitioned table are filtered out.
To fix this issue we make sure that the estimated result cardinality of
the scan node is zero when all the partitions are filtered out.

Change-Id: I225949eb2e8f905a5d0f678d7f199fb95ba4aab0
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3063
Reviewed-by: Dimitris Tsirogiannis <dtsirogiannis@cloudera.com>
Tested-by: jenkins