Summary:
Part 2 of changing flipper to use customizable ports: iOS SDK.
Still to go: JS app.
env var should be of the format:
`FLIPPER_PORTS=1111,2222` for insecure port: 1111 and secure port: 2222.
Reviewed By: danielbuechele
Differential Revision: D13800988
fbshipit-source-id: 3560ba850389964f4b784551b803c45c6524e6f0
