IMPALA-932: evaluate concat/concat_ws children once
IMPALA-932: evaluate concat/concat_ws children once

Change-Id: Id22a6c1dfb57cf659a1e24af4de6e5a2336cafa4
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2152
Reviewed-by: Skye Wanderman-Milne <6d4b168ab637b0a20cc9dbf96abb2537f372f946@cloudera.com>
Tested-by: jenkins
(cherry picked from commit cf6960017d4f7d75c1c685cf362bd3d9cd9b63c7)
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2183

michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala