gsupplicant: use term managed in object path

gsupplicant: use term managed in object path

gsupplicant uses term "infra" instead of "managed" used by the old
wifi plugin. This forced connman to create a new service instead of using
the stored. For example, wifi_0026b6675606_76616c6f_managed_psk
vs wifi_0026b6675606_76616c6f_infra_psk.

Convert gsupplicant to use term "managed". That way old services work with
the new plugin.