FAILURE CREATING COMPOSITE FKS BASED ON UNIQUE INDEXES

If the child/parent index of an FK is an UniqueHashIndex, it
has to be based on the exact same columns as that of the
FK's child/parent columns. The column order doesn't matter.

But ha_ndbcluster::find_matching_index() was returning
UniqueHashIndexes even if there was a partial match and the
column count didn't match up. This creates a problem during
composite FK creation.

This patch fixes it by returning UniqueHashIndexes only if
there is a complete match - the UniqueHashIndex is based on
the exact same columns as the FK's parent/child column list.
This patch also includes testcases for the fix.