RESTART/REBUILD

Analysis
========

When restarting MySQL or rebuilding the table, all partitions will
initially have 'update_time' set to NULL. When a partition is updated,
'update_time' for all partitions with a higher ordinal position will
also be updated. Function store_schema_partitions_record() doesn't mark
the 'update_time' field as NULL, when 'update_time' for the partition is
ZERO. This causes get_schema_partitions_record() to use previous partition
'update_time'.

Fix
===

The function 'store_schema_partitions_record()' now sets the 'update_time'
to NULL, if it is set to zero in InnoDB.

Change-Id: I25cb844e258342f4d73e264c6767c1319e915326