Merge ~twom/launchpad:fix-vitals-tests into launchpad:master

[Tom Wardill]

testfix: Ensure vitals_map exist

`updateStats` is on a timer, and requires the `vitals_map` attribute of `PrefetchedBuilderFactory` to exist. This is currently only created in the `update` method, so it's possible to race if `updateStats` is called first.
Add an init to `PrefetchedBuilderFactory` and create `vitals_map` in it.

[Colin Watson (cjwatson)]

review: Approve

diff --git a/lib/lp/buildmaster/manager.py b/lib/lp/buildmaster/manager.py
index 3ace0d8..fb9baaa 100644
--- a/lib/lp/buildmaster/manager.py
+++ b/lib/lp/buildmaster/manager.py
@@ -257,6 +257,12 @@ class PrefetchedBuilderFactory(BaseBuilderFactory):
     from cached data updated by `update`.
     """
 
+    def __init__(self, *args, **kwargs):
+        super(PrefetchedBuilderFactory, self).__init__(*args, **kwargs)
+        # This needs to exist to avoid race conditions between
+        # `updateStats` and `update`.
+        self.vitals_map = {}
+
     def update(self):
         """See `BaseBuilderFactory`."""
         transaction.abort()