Carrier confirmation code.

If confirmation code is null and required during downloading a profile,
returns a resovable error, and show ConfirmationCodeActivity. After we
get the confirmation code from the user, continue the operation.

Add the confirmationCode as a member in DownloadableSubscription.

Test: unit test, e2e on phone
Bug: 36730837
Change-Id: Id649e0623f582ce3fc2f2eb8db01e4502f72ff5b