Add exo_unittests to "Cast Linux" bots

Bug: 896710
Test: Ran exo_unittests locally to verify they work.
Change-Id: I7d015adeaf762bc7c4b1b1a5f9955f93d2dea26c
Reviewed-on: https://chromium-review.googlesource.com/c/1340902
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615298}
3 files changed