Improve CI

Add more tests to the CI, including a docker build test, and add the
generation and publication of a new docker image on master and tags

.drone.yml

@@ -1,3 +1,4 @@
+---
 # Test building the code and docker image
 kind: pipeline
 type: docker
@@ -46,6 +47,7 @@ trigger:
   event:
     - push
 
+---
 # On a tag, only build the related docker image
 kind: pipeline
 type: docker
@@ -66,3 +68,5 @@ steps:
 trigger:
   event:
     - tag
+
+...