Give better error description in check_valid_gerrit_projects.py
Give better error description in check_valid_gerrit_projects.py

This error message was confusing, make it clearer.

Change-Id: Ia930483a8b36f75610a5de711b22b553410d5ff8

Tesora/tesora-project-config,openstack-infra/project-config,Tesora/tesora-project-config,openstack-infra/project-config