Starts a host process to receive logcat output over vsock

The host process is started conditionally on the logcat_mode launcher
flag (when set to 'vsock'). The process accepts connections (one at a
time) on a vsock socket and forwards everything to the logcat file in
the instance directory.

Bug: 124535805
Test: run locally
Change-Id: I2dbff42735a9dc16079e8adb5862ead3c7581de4