IMPALA-1257: Fix asan issue with string literals.

Change-Id: I31a24a3323081b6486bf7baf450f8fb2fdc56ec5
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4363
Reviewed-by: Ippokratis Pandis <ipandis@cloudera.com>
Tested-by: jenkins