Clark Boylan a08516c488 Switch nodes to xenial
These nodes no longer run on trusty and should be tested on xenial.

Change-Id: Iae4dc7798b43f74c183ca55c3f05d1f3d97f0a9f
2019-12-10 15:59:34 -08:00
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2019-12-10 15:59:34 -08:00