On older devices it might happen that lockdownd does not return any result,
neither success nor failure, when invoking lockdownd_activate(). This results
in the code to assume the operation failed.
Instead of relying on the return value of that function we query the actual
ActivationState to see if it is not "Unactivated" anymore to determine if the
activation was successful.

For some reason, asking lockdownd for 'InternationalMobileSubscriberIdentity'
sometimes returns "MissingValue", even though ideviceinfo (without passing a
key) shows it.
This commit changes the code to get the whole lockdownd 'NULL domain' info
(equivalent to ideviceinfo without specifying any key) and parse the required
info from there.