3 occasions of 2 sporadic failures in ci logs as of 5pm friday

seen at
https://ci.mozilla.org/view/Persona/job/identity.browserid.dev.windows.x
p.ie.8/1315/testReport/junit/123done.tests.test_new_user/TestNewAccount/
test_can_create_new_user_account

self = <browserid.pages.sign_in.SignIn object at 0x188cf10>

    def close_window(self):
>       self.selenium.close()

browserid/pages/sign_in.py:53:

E       WebDriverException: Message: u'ERROR Internal Server Error'

------------

seen at
https://ci.mozilla.org/view/Persona/job/identity.browserid.dev.windows.7
.ie.9/1324/testReport/junit/123done.tests.test_sign_in/TestSignIn/test_t
hat_user_can_sign_in/

https://ci.mozilla.org/view/Persona/job/identity.browserid.dev.windows.7
.ie.9/1313/testReport/junit/123done.tests.test_change_password/TestChang
ePassword/test_can_change_user_password/

self = <browserid.pages.sign_in.SignIn object at 0x2a3ff10>
selenium = <selenium.webdriver.remote.webdriver.WebDriver object at
0x29b9bd0>
timeout = 90, expect = 'new'

    def __init__(self, selenium, timeout, expect='new'):
        Base.__init__(self, selenium, timeout)

>       selenium.switch_to_window('__persona_dialog')

browserid/pages/sign_in.py:38:

E       NoSuchWindowException: Message: u"No window found