stepToWaitForSwitchWithAccessibilityLabel:value: for easier verification of UISwitch value

stepToWaitForViewWithAccessibilityLabel:value:traits: works for checking the value of a UISwitch, but I suspect that people need to do some extra typing (switchIsOn ? @"1" : @"0") to provide the value as a string. The implementation is mostly copied from stepToSetOn:forSwitchWithAccessibilityLabel:.