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 <skye@cloudera.com>
Tested-by: jenkins
IMPALA-922: Return helpful errors with Yarn group rules

When the -fair_scheduler_allocation_path is configured with a policy that uses
the "primaryGroup" Yarn queue allocation rule, Yarn throws an error if the user
is not on the local OS. Currently the user will get an error message that says:
"java.io.IOException: No groups found for user <username>". We now return a more
helpful error message.

Change-Id: I014ac15ef607e473957752f23af94d0cc4efec0f
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2078
Reviewed-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: jenkins
IMP-1329,IMPALA-924: Make ExchangeNode::Open() block until rows are available.

The bug: Coordinator::Wait() is supposed to block until rows become available for
consumption by the client. We rely on Wait() to determine when to advance the query
status to a 'ready' state and signal to the client that rows can be fetched.
Long fetch times can trigger client timeouts at various levels (socket, app, etc.).
Coordinator::Wait() simply opens the coordinator fragment's plan tree.
For most plan nodes, Open() does work to prepare the plan tree, s.t., GetNext()
returns quickly. However, for ExchangeNodes Open() used to not wait
until rows are obtained form the underlying stream receiver.
The fix: Make ExchangeNode::Open() block until rows are available.

Change-Id: I7b197eea11d21fd732414d96c899a17b2d99631c
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2128
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins