Avoid crash in master on early failure
Avoid crash in master on early failure

An early failure in a test job using notifications can fail if
self.notifications.blacklist is None.

Change-Id: I7f9058329985630d2833e195dee7012797fc4546

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server