kojiapi: support multi-build composes

This removes the restriction of only having a single build per compose
and uses the new job types to schedule the broken-appart build.

A small change in behavior is introduced: the koji build ID is not
known when the call to `compose` returns, so it is always set to
`0`. In the future we should remove this from the API, and instead
rely on the status call to return this information, when it is
known.

The status route will be updated in follow-up commits to reflect the
changes introduced here.

tools/koji-compose.py

@@ -40,6 +40,10 @@ def compose_request(distro, koji, arch):
             "architecture": "x86_64",
             "image_type": "qcow2",
             "repositories": repositories
+        },{
+            "architecture": "x86_64",
+            "image_type": "ami",
+            "repositories": repositories
         }]
     }