If _update_from_compute_node returns early and the HostState is
not filtered out we can hit an AttributeError in the
BuildFailureWeigher because the failed_builds attribute is not
set. This simply initializes the attribute like the other stats
fields.
Change-Id: I5f8e4d32c6a1d6b61396b4fa11c5d776f432df0c
Closes-Bug: #1834691
(cherry picked from commit d540903463)