Install factory tests onto factory test images

Make this happen by emerging the autotest-factory-install
package into the image.  This installs the set of tests
needed by factory images.

TEST=Buildbots and inspection
BUG=chromium:313960

CQ-DEPEND=CL:62089

Change-Id: Ie2a49dac3ca93d25ee57538191f30786538e2a0a
Reviewed-on: https://chromium-review.googlesource.com/177372
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
8 files changed