Support arbitrary addresses in adb_connector.

Before it only supported maintaining a connection to ports, and would
internally add 127.0.0.1: as a prefix. This is in preparation for
supporting vsock addresses as well as TCP addresses.

Bug: 121166534
Test: Ran adb in tunnel mode.
Change-Id: Ib383a708068f1e320d76873e52d67217b743656a