integration-cli: use remote daemon in proxy test

TestCliProxyDisableProxyUnixSock runs `docker info` by
clearing env however if the daemon is set up to run in a
different machine (e.g. Windows CI case) it does not make
use of DOCKER_TEST_HOST and tries to connect unix sock.

This fix injects DOCKER_HOST back to the test.

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>