Increase PyAuto UnlockScreen() timeout.
Increase PyAuto UnlockScreen() timeout.

We believe that desktopui_ScreenLocker is flaky because unlocking the screen can take longer than the automation timeout. If that's the case, increasing the timeout will fix it!

BUG=chromium-os:19840
TEST=Autotest desktopui_ScreenLocker, PyAuto chromeos_login.ChromeosLogin.testLockAndUnlockScreenAfterLogin

Review URL: http://codereview.chromium.org/7756024

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@99109 0039d316-1c4b-4281-b951-d872f2087c98

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