Intermittent test failures due to Chrome errors

Certain test runs are failing because Chrome is not reachable.

For example, on this build: https://travis-ci.org/panopoly/panopoly/builds/55168502

Jobs #9-11 and 15-20 are failing, but the rest are passing. The whole Chrome suite doesn't run. The error is:

[Behat\Mink\Exception\DriverException]
Exception has been thrown in "beforeStep" hook, defined in FeatureContext::beforeJavascriptStep()
Could not open connection
[WebDriver\Exception\UnknownError]
chrome not reachable
(Driver info: chromedriver=2.9.248304,platform=Linux 2.6.32-042stab090.5 x86_64) (WARNING: The server did not provide any stacktrace information)
Command duration or timeout: 60.56 seconds
Build info: version: '2.41.0', revision: '3192d8a', time: '2014-03-27 17:17:32'
System info: host: 'testing-worker-linux-c55820f2-1-522-linux-2-55168511', ip: '127.0.0.1', os.name: 'Linux', os.arch: 'amd64', os.version: '2.6.32-042stab090.5', java.version: '1.7.0_76'
Driver info: org.openqa.selenium.chrome.ChromeDriver

Looks like it might be caused by an error in the system-install task? On a failing job, I see this:

** Setting up APT
+wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub
+sudo apt-key add -
OK
+sudo sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list'
+sudo apt-get update
W: GPG error: http://dl.google.com stable Release: The following signatures were invalid: BADSIG A040830F7FAC5991 Google, Inc. Linux Package Signing Key <linux-packages-keymaster@google.com>
+mysql -e 'create database drupal;'

Whereas on a passing job, I see this:

** Setting up APT
+wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub
+sudo apt-key add -
OK
+sudo sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list'
+sudo apt-get update
+mysql -e 'create database drupal;'