Use LOG.exception instead of LOG.error for debug
Use LOG.exception instead of LOG.error for debug

This patch changes a LOG call from LOG.error to LOG.exception so that
the developer/operator can check the detailed call stack.

Change-Id: I26ae7eb18c89eb76d4d155929e77d6a998c28b58

stackforge/senlin,stackforge/senlin,openstack/senlin,openstack/senlin,Alzon/senlin,tengqm/senlin-container,Alzon/senlin,openstack/senlin,tengqm/senlin-container