IMPALA-1011: Handle SHOW DATA SOURCES when no sources configured

Change-Id: I367b90c7603aea973d442f9186a6b32598a66a28
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2716
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins
IMPALA-959: Fix ASAN decimal crashes.

Not quite sure what the underlying issue is but these fixes seem to work.

Change-Id: I759804eb8338ba86969c0214a1e6e35588c94297
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2698
Reviewed-by: Marcel Kornacker <marcel@cloudera.com>
Tested-by: jenkins