[Fuchsia] Symbolize stderr in blink web tests

Previously call stacks from crashed web tests wasn't symbolized properly.
Updated the scripts to run the symbolizer as a stderr filter, which
makes it easier to debug layout test crashes.

Also fixed file descriptor leak in run_package.py

Change-Id: I2622865ab930535567b16e70ca9e50610a93761f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1584779
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654220}
3 files changed