[18.09 backport] fix panic on empty dockerfile

[thaJeztah]

• bump buildkit 05766c5c21a1e528eeb1c3522b2f05493fe9ac47 (docker-18.09 branch)
  • [18.09 backport] Have parser error on dockerfiles without instructions moby/buildkit#952 [18.09 backport] Have parser error on dockerfiles without instructions
    • backport of Have parser error on dockerfiles without instructions moby/buildkit#771 Have parser error on dockerfiles without instructions
• Error on empty dockerfile moby/moby#38487 Error on empty dockerfile
  • first two commits (last commit (vendor bump) is replaced with the bump above)

[thaJeztah]

ping @tonistiigi @LinuxMercedes ptal

[LinuxMercedes]

The failures looks unrelated:

12:00:36 FAIL: docker_cli_pull_test.go:270: DockerSuite.TestPullWindowsImageFailsOnLinux
12:00:36 
12:00:36 docker_cli_pull_test.go:273:
12:00:36     c.Assert(err.Error(), checker.Contains, "cannot be used on this platform")
12:00:36 ... obtained string = "" +
12:00:36 ...     "\n" +
12:00:36 ...     "Command:  /usr/local/cli/docker pull microsoft/nanoserver\n" +
12:00:36 ...     "ExitCode: 1\n" +
12:00:36 ...     "Error:    exit status 1\n" +
12:00:36 ...     "Stdout:   Using default tag: latest\n" +
12:00:36 ...     "\n" +
12:00:36 ...     "Stderr:   Error response from daemon: manifest for microsoft/nanoserver:latest not found\n" +
12:00:36 ...     "\n" +
12:00:36 ...     "\n" +
12:00:36 ...     "Failures:\n" +
12:00:36 ...     "ExitCode was 1 expected 0\n" +
12:00:36 ...     "Expected no error"
12:00:36 ... substring string = "cannot be used on this platform"

[thaJeztah]

The failures looks unrelated:

Ah, yes, I forgot the fix for that isn't merged yet; the fix for that is included in #198 😓

[LinuxMercedes]

Ah!

Looks good otherwise! 👍

[thaJeztah]

rebased, now that #198 was merged

[LinuxMercedes]

Failures so far look flaky:

• z: [epic] flaky tests moby/moby#37306 (TestServiceRemoveKeepsIngressNetwork)
• experimental: Flaky test: TestStartReturnCorrectExitCode moby/moby#38521

[LinuxMercedes]

Oh, that janky failure is related. You'd need to include moby#38524 or backport docker/docker-py#2216 to whatever version of docker-py is included in this release.

[thaJeztah]

Oh, good catch thanks! opened a separate PR for that one #202

[thaJeztah]

rebased on top of #202 to get both changes in here

[andrewhsu]

LGTM