Do not run consolidator if userExtSource is known

If users goes throung chain applications form (for VO and then for group),
then after submiting application for VO the new user is created, but the
perunSession isn't refreshed, therefore checkForSimilarUsers found newly
created user.

This commit fix checkForSimilarUsers. It return no match, if it found
user base on extSource and extLogin from session.