Extend job list when inheriting jobs

The append was adding the inherited jobs as a whole list, resulting
in a job list of mixed type (job and list). This was obviously throwing
errors when the job list was parsed.

Change-Id: I0b61c2466bf1e32ec62bbcb5d3323e09ad3a040b
Signed-off-by: Jesse Keating <omgjlk@us.ibm.com>
diff --git a/zuul/model.py b/zuul/model.py
index c2b4a9a..f7aa8f9 100644
--- a/zuul/model.py
+++ b/zuul/model.py
@@ -946,7 +946,7 @@
     def inheritFrom(self, other):
         for jobname, jobs in other.jobs.items():
             if jobname in self.jobs:
-                self.jobs[jobname].append(jobs)
+                self.jobs[jobname].extend(jobs)
             else:
                 self.jobs[jobname] = jobs