Sort the list of roles when they're presented for selection

[RonRothman]

The main benefit is that lexicographically similar roles (e.g. same AWS account) will be adjacent, reducing errors. For example, what is currently presented this way:

[  1] arn:aws:iam::13856293331:role/admin
[  2] arn:aws:iam::20922837461:role/admin
[  3] arn:aws:iam::13856293331:role/eng/dev

would be presented this way:

[  2] arn:aws:iam::20922837461:role/admin
[  1] arn:aws:iam::13856293331:role/admin
[  3] arn:aws:iam::13856293331:role/eng/dev

[coveralls]

Coverage remained the same at 47.536% when pulling cbc96d7 on RonRothman:sort_roles_prompt into d473d67 on cevoaustralia:master.