Make the emulated VHAL always listen for socket connections.

Previously, when running under the emulator, it would only connect to
the emulator's qemu pipe and you couldn't script the emulated VHAL.

Also changed the logic of SocketComm so that it supports connections
from more than one client at a time.

Bug: 87643732
Test: tested locally
Change-Id: I504cd806f0a95799a68b75c3515c1f230109f1d0
(cherry picked from commit 8dad67a0148114cb60f3567268bc2cf40ff18f82)