packaging: setup: Making error messages more verbose

Making error messages a bit more verbose to help the user
pointing out possible problems.

Change-Id: I7b7201b23adbb0ee7c452f9a936644b2b7b52ac4
Bug-Url: https://bugzilla.redhat.com/1146070
Signed-off-by: Simone Tiraboschi <stirabos@redhat.com>