Improve get_unique(preclude=True) error message
Improve get_unique(preclude=True) error message

The existing object may belong to a subclass of the base class of the
query. Report the real class name of the object instead of the name of
the base of the query.

Reviewed-By: Wesley Hertlein <ca32100e9f664971b15d1470ddc7f009d907efd3@morganstanley.com>

stdweird/aquilon,stdweird/aquilon,quattor/aquilon,quattor/aquilon,guillaume-philippon/aquilon,quattor/aquilon,guillaume-philippon/aquilon,guillaume-philippon/aquilon,stdweird/aquilon