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.

Merged-In: Ibe1e0fc5ddb736b411faf48ec9bea3c68972bb99
Test: unit test, e2e on phone
Bug: 36730837
Change-Id: Ibe1e0fc5ddb736b411faf48ec9bea3c68972bb99