docker_cli_run_test: Preserve DOCKER_TEST_HOST in env-clearing tests

For Windows, we run integration-cli with DOCKER_TEST_HOST env var b/c
daemon is on some remote machine. This keeps the DOCKER_HOST set by
bash scripts in the env.

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

integration-cli/docker_utils.go

@@ -893,3 +893,13 @@ func setupRegistry(t *testing.T) func() {
 
 	return func() { reg.Close() }
 }
+
+// appendDockerHostEnv adds given env slice DOCKER_HOST value if set in the
+// environment. Useful when environment is cleared but we want to preserve DOCKER_HOST
+// to execute tests against a remote daemon.
+func appendDockerHostEnv(env []string) []string {
+	if dockerHost := os.Getenv("DOCKER_HOST"); dockerHost != "" {
+		env = append(env, fmt.Sprintf("DOCKER_HOST=%s", dockerHost))
+	}
+	return env
+}