Updating test-code only; set ReadHeaderTimeout for some, or suppress the linter
error for others.

     contrib/httpserver/server.go:11:12: G114: Use of net/http serve function that has no support for setting timeouts (gosec)
        log.Panic(http.ListenAndServe(":80", nil))
                  ^
     integration/plugin/logging/cmd/close_on_start/main.go:42:12: G112: Potential Slowloris Attack because ReadHeaderTimeout is not configured in the http.Server (gosec)
        server := http.Server{
            Addr:    l.Addr().String(),
            Handler: mux,
        }
     integration/plugin/logging/cmd/discard/main.go:17:12: G112: Potential Slowloris Attack because ReadHeaderTimeout is not configured in the http.Server (gosec)
        server := http.Server{
            Addr:    l.Addr().String(),
            Handler: mux,
        }
     integration/plugin/logging/cmd/dummy/main.go:14:12: G112: Potential Slowloris Attack because ReadHeaderTimeout is not configured in the http.Server (gosec)
        server := http.Server{
            Addr:    l.Addr().String(),
            Handler: http.NewServeMux(),
        }
     integration/plugin/volumes/cmd/dummy/main.go:14:12: G112: Potential Slowloris Attack because ReadHeaderTimeout is not configured in the http.Server (gosec)
        server := http.Server{
            Addr:    l.Addr().String(),
            Handler: http.NewServeMux(),
        }
     testutil/fixtures/plugin/basic/basic.go:25:12: G112: Potential Slowloris Attack because ReadHeaderTimeout is not configured in the http.Server (gosec)
        server := http.Server{
            Addr:    l.Addr().String(),
            Handler: http.NewServeMux(),
        }
     volume/testutils/testutils.go:170:5: G114: Use of net/http serve function that has no support for setting timeouts (gosec)
        go http.Serve(l, mux)
           ^

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

For obvious reasons that it is not really supported now.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

Signed-off-by: Amit Krishnan <krish.amit@gmail.com>

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

Implemented a FakeStorage alternative that supports spinning
up a remote container on DOCKER_TEST_HOST to serve files over
an offline-compiled Go static web server image so that tests which
use URLs in Dockerfile can build them over at the daemon side.

`fakeStorage` function now automatically chooses if it should
use a local httptest.Server or a remote container.

This fixes the following tests when running against a remote
daemon:

- `TestBuildCacheADD`
- `TestBuildCopyWildcardNoFind`
- `TestBuildCopyWildcardCache`
- `TestBuildADDRemoteFileWithCache`
- `TestBuildADDRemoteFileWithoutCache`
- `TestBuildADDRemoteFileMTime`
- `TestBuildADDLocalAndRemoteFilesWithCache`
- `TestBuildADDLocalAndRemoteFilesWithoutCache`
- `TestBuildFromURLWithF`
- `TestBuildApiDockerFileRemote`

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