[Impala-CR](cdh5-trunk) IMPALA-3385: Fix crashes on accessing error_log

["Huaisi Xu (Code Review)" <ge...@cloudera.org>]

Huaisi Xu has uploaded a new patch set (#2).

Change subject: IMPALA-3385: Fix crashes on accessing error_log
......................................................................

IMPALA-3385: Fix crashes on accessing error_log

We used to check error_log empty with error_log.empty(), but
this may return false even when some of its member has empty
messages, thus crashes impala.

This commit:

1. Make sure that messeges vecters are always
non-empty when accessed.

2. Remove error_log from hdfsScanNode::splitprocess since the
logs may contain irrelevant errors. This also prevents a
potential race condition when error_log is checked and enters
if clause, but later is changed by other threads.

3. Hold locks when returning error_log.

4. Added guarantee that TErrorLogEntry::count is 0 on construction.

Change-Id: I3a7e3d22e26147ada780aae5aed1f2e25a515afc
---
M be/src/exec/hdfs-scan-node.cc
M be/src/runtime/runtime-state.cc
M be/src/runtime/runtime-state.h
M be/src/util/error-util.cc
M common/thrift/ImpalaInternalService.thrift
5 files changed, 13 insertions(+), 15 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala refs/changes/29/2829/2
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I3a7e3d22e26147ada780aae5aed1f2e25a515afc
Gerrit-PatchSet: 2
Gerrit-Project: Impala
Gerrit-Branch: cdh5-trunk
Gerrit-Owner: Huaisi Xu <hx...@cloudera.com>
Gerrit-Reviewer: Bharath Vissapragada <bh...@cloudera.com>
Gerrit-Reviewer: Dan Hecht <dh...@cloudera.com>
Gerrit-Reviewer: Huaisi Xu <hx...@cloudera.com>