docker run, create: don't swallow connection errors during validate

Some validation steps done by `docker create` (and `docker run`) are platform-
specific, and need to know the daemon's OS.

To get this information, the CLI.ServerInfo() method was used, which
discards connection errors, resulting in an empty OS, which causes
validation to fail with an "unknown server OS" error message.

This patch changes it to use the Client.Ping so that we can error when
failing to connect.

We should look if we can reduce the platform-specific validation and parsing
on the client-side, but at least this change should produce a more useful
error.

Before this patch:

    DOCKER_HOST=tcp://example.invalid docker run -it --rm --device=/dev/dri alpine
    docker: unknown server OS:

    Run 'docker run --help' for more information

With this patch:

    DOCKER_HOST=tcp://example.invalid docker run -it --rm --device=/dev/dri alpine
    failed to connect to the docker API at tcp://example.invalid:2375: lookup example.invalid on 192.168.65.7:53: no such host

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/container/client_test.go

@@ -232,3 +232,7 @@ func (f *fakeClient) ContainerPause(ctx context.Context, containerID string, opt
 
 	return client.ContainerPauseResult{}, nil
 }
+
+func (*fakeClient) Ping(_ context.Context, _ client.PingOptions) (client.PingResult, error) {
+	return client.PingResult{}, nil
+}

cli/command/container/create.go

@@ -112,7 +112,12 @@ func runCreate(ctx context.Context, dockerCli command.Cli, flags *pflag.FlagSet,
 		}
 	}
 	copts.env = *opts.NewListOptsRef(&newEnv, nil)
-	containerCfg, err := parse(flags, copts, dockerCli.ServerInfo().OSType)
+	serverInfo, err := dockerCli.Client().Ping(ctx, client.PingOptions{})
+	if err != nil {
+		return err
+	}
+
+	containerCfg, err := parse(flags, copts, serverInfo.OSType)
 	if err != nil {
 		return cli.StatusError{
 			Status:     withHelp(err, "create").Error(),

cli/command/container/run.go

@@ -101,7 +101,12 @@ func runRun(ctx context.Context, dockerCli command.Cli, flags *pflag.FlagSet, ro
 		}
 	}
 	copts.env = *opts.NewListOptsRef(&newEnv, nil)
-	containerCfg, err := parse(flags, copts, dockerCli.ServerInfo().OSType)
+	serverInfo, err := dockerCli.Client().Ping(ctx, client.PingOptions{})
+	if err != nil {
+		return err
+	}
+
+	containerCfg, err := parse(flags, copts, serverInfo.OSType)
 	// just in case the parse does not exit
 	if err != nil {
 		return cli.StatusError{