Allow test apks to run even when test server spawning fails

For remote forwarded android devices, spawning the test server fails,
but most tests seem to pass anyways, so for local development we can
just log an error and continue.

Bug: 1030827
Change-Id: I24610348a785a2bdf3715a0cc87518c70cbafd10
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2174959
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#764827}