Support multiple roles in instance profile credentials

[lwoggardner]

I am about to embark on some cross account work that I think will require my instance profiles to be provided with multiple roles.

I note that the current instance profile credentials simply chooses the first role returned in the metadata under '/latest/meta-data/iam/security-credentials/'

If you have multiple roles I'm not even sure this will return the same one each time, but in any case it would be good to have an option to select a specific role.

I will have an attempt at creating a patch for this myself but thought it would be good to raise it here first.

[lwoggardner]

OK, the fine print around instance roles makes it clear that only one role is current possible.