rdbms: set cpPosIndex to null in ChronologyProtector::shutdown on failure

rdbms: set cpPosIndex to null in ChronologyProtector::shutdown on failure

This already happens on lock acquisition failure but not on write failure.
If the write failed, then there is not point timing out on the next request
after waiting "waitForPosStoreTimeout" seconds.

Also raise the initPositions() logging for missing positions to WARNING
and improve the wait loop log entries in that method.

Change-Id: Id738eb6f85c91dd05fadd2e6c3f19ae3204e2575