Be explicit about using Podman in CI build.

.drone.yml

@@ -8,12 +8,15 @@ steps:
 - name: build
   image: plugins/docker
   settings:
-    username:
+    USERNAME:
       from_secret: docker_username
-    password:
+    PASSWORD:
       from_secret: docker_password
-    registry: projects.torsion.org
-    repo: projects.torsion.org/witten/mediagoblin-docker
+    IMAGE_NAME: projects.torsion.org/witten/mediagoblin-docker
+  commands:
+    - podman login --username "$USERNAME" --password "$PASSWORD" projects.torsion.org
+    - podman build --tag "$IMAGE_NAME" --storage-opt "overlay.mount_program=/usr/bin/fuse-overlayfs" .
+    - podman push "$IMAGE_NAME"
 
 trigger:
   repo: