Fixed issue of product catalog-variants not being available. #6504

The issue was with exact-matching of attributes being done on the
front-end. The solution was to
* Either relax the matching (via underscoreJS) OR
* Send only those variation attributes to the front-end which are actually specified in the Variation Attributes section of the template.
Approach 2 has been applied.
dict(filter(lambda attr: attr[0] in va, attributes.iteritems()))