Add getAvailableNetworks.

To allow a operator test to pass we need to manually select
a network. Therefore getAvailableNetworks needs to be implemented
on CDMALTEPhone so that RIL_REQUEST_QUERY_AVAILABLE_NETWORKS is
sent to the RIL/radio.

Bug: 5420630
Change-Id: I8e138b211d42755399a9e30f3e45dde2f579401e