Fix deprecation warnings is southbound-impl

Fix deprecation warnings is southbound-impl

Use BindingMap.Builder to replace ArrayList, which maintains
is almost a drop-in replacement. While we are in the area, also
fix duplicate invocations of SouthboundMapper.

Since the interactions take advantage of what builders provide,
also ditch a ton of mocking in favor of using provided builder
implementation.

Change-Id: I4bd4a86039b8ef3159091565be2581b9fe23aefc
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>