I successfully ran the mobile-web test on and iPhone Simulator. I am currently trying to run the ios_simple.py test.
EDIT: Ok so the problem seems to be that an alert pop ups saying "this app may slow your iPhone etc etc". I tried dismissing it with adding 'autoAcceptAlerts': 'true' in desired capabilities which doesn't seem to work.
desired_capabilities={
'app': app,
'platformName': 'iOS',
'platformVersion': '10.1',
'deviceName': 'iPhone Simulator',
'autoAcceptAlerts': 'true'
}