packaging: configuration cleanups

- install imageuploader.conf with 0640 access mode
- avoid to install hidden empty files for creating an empty
  configuration directory

Change-Id: Idb1559da5d95e723d4b9c2b45760a71700d865f8
Bug-Url: https://bugzilla.redhat.com/1058810
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>