goldfish-opengl: open rendernode in HostConnection

In the long-term, it makes sense to separate the concept of a "device"
from a "stream".  The virtio-gpu device may be used to create a stream
via memory management options, but also does a few other things (like
fence creation).

This is one incremental refactor towards that concept.

BUG=202552093
TEST=run gfxstream

Change-Id: I4988a15135659777bd68892ab71c3e4912c83850
5 files changed