Submit credit card membership flow ignores payment processor payment status if membership is recurring

Some payment processors (IATS, also possibly eWay?) return a contribution status id. This is ignored when submitting a membership via credit card if the membership is recurring. Therefore the initial payment gets created as pending even if it was successful and the membership is also pending.

To reproduce:

• Setup the IATS processor with the test credentials.
• See https://github.com/iATSPayments/com.iatspayments.civicrm/blob/master/README.md for those
• Create a membership type with fees that will validate with the test processor EG. $3.00/mth and with the auto-recur option.
• In the backend submit a credit card membership and choose to have it automatically recur. (Use the test visa 4111111111111111 etc.)
• Even though the first payment goes through in the payment processor backend the payment is pending and so is the membership

I have attached a patch which is my first naive attempt to fix it. I haven't tested it thoroughly at all yet including how it affects processors other than IATS.