Switch to drone-fossa plugin

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>

.drone.yml

@@ -23,16 +23,11 @@ steps:
     path: /var/run/docker.sock
 
 - name: fossa
-  image: registry.suse.com/suse/sle15:15.3.17.8.1
+  image: rancher/drone-fossa:latest
   failure: ignore
   environment:
     FOSSA_API_KEY:
       from_secret: FOSSA_API_KEY
-  commands:
-    - zypper -n install curl unzip
-    - "curl -H 'Cache-Control: no-cache' https://raw.githubusercontent.com/fossas/spectrometer/master/install.sh | sh"
-    - fossa analyze
-    - fossa test
   when:
     instance:
       - drone-publish.k3s.io