Unstash rhel8nightly repo & json files

- even if they don't exist sometimes but ignore the errors
- make the nightly repository with a higher priority
- override rhel-8*.json files so that newly built images will
  also consume the nightly content

tools/provision.sh

@@ -30,6 +30,15 @@ case "${ID}-${VERSION_ID}" in
     *) ;;
 esac
 
+# overrides for RHEL nightly builds testing
+if [ -f "rhel-8.json" ]; then
+    sudo mv rhel-8.json /etc/osbuild-composer/repositories/
+fi
+
+if [ -f "rhel-8-beta.json" ]; then
+    sudo mv rhel-8-beta.json /etc/osbuild-composer/repositories/
+fi
+
 # Generate all X.509 certificates for the tests
 # The whole generation is done in a $CADIR to better represent how osbuild-ca
 # it.