Correctly show the error on non-leader
Correctly show the error on non-leader

When non-leader tries to invite, print the error rather than unhelpful
exception with no helpful data.

jjohnson42/confluent,xcat2/confluent,jjohnson42/confluent,xcat2/confluent,jjohnson42/confluent,whowutwut/confluent,jjohnson42/confluent,xcat2/confluent,jjohnson42/confluent,whowutwut/confluent,whowutwut/confluent,xcat2/confluent,xcat2/confluent,whowutwut/confluent