Expose buildset to the executor and url formatter

For github (and probably other providers) we really only have the option
of returning 1 url for the entire buildset, as opposed to 1 per build.
To make log uploading within that easier we really need a way to
globally identify all the different builds that belong to 1 change.

The zuul ref is already available however this is a concept that is
planned to be deprecated, so instead add a UUID parameter to the
buildset that we can pass through. This UUID is used to build the ref to
make migration easier.

Change-Id: I1cab8af5c9d7f6875591fbe4ac4e184b90f6ca12
Signed-off-by: Jamie Lennox <jamielennox@gmail.com>
diff --git a/tests/fixtures/layouts/reporting-github.yaml b/tests/fixtures/layouts/reporting-github.yaml
index 43e71c7..d054df7 100644
--- a/tests/fixtures/layouts/reporting-github.yaml
+++ b/tests/fixtures/layouts/reporting-github.yaml
@@ -29,7 +29,7 @@
       github:
         comment: false
         status: 'success'
-        status-url: http://logs.example.com/{tenant.name}/{pipeline.name}/{change.project}/{change.number}/{change.patchset}/
+        status-url: http://logs.example.com/{tenant.name}/{pipeline.name}/{change.project}/{change.number}/{buildset.uuid}/
     failure:
       github:
         comment: false