[19.03 backport] Builder: fix "COPY --from" to non-existing directory on Windows [ENGCORE-935]

[thaJeztah]

backport of:

• make.ps1: Run-IntegrationTests(): set working directory for test suite moby/moby#39698 make.ps1: Run-IntegrationTests(): set working directory for test suite
• Builder: fix "COPY --from" to non-existing directory on Windows moby/moby#39695 Builder: fix COPY --from to non-existing directory on Windows

fixes docker/for-win#4349
built on top of moby#39698

This fixes a regression introduced in 6d87f19 (moby#38599),
causing COPY --from to fail if the target directory does not exist:

FROM mcr.microsoft.com/windows/servercore:ltsc2019 as s1
RUN echo "Hello World" > /hello

FROM mcr.microsoft.com/windows/servercore:ltsc2019
COPY --from=s1 /hello /hello/another/world

Would produce an error:

Step 4/4 : COPY --from=s1 /hello /hello/another/world
failed to copy files: mkdir \\?: The filename, directory name, or volume label syntax is incorrect.

The cause for this was that Go's os.MkdirAll() does not support/detect volume GUID paths
(\\?\Volume{dae8d3ac-b9a1-11e9-88eb-e8554b2ba1db}\hello\another}), and as a result
attempted to create the volume as a directory (\\?), causing it to fail.

This patch replaces os.MkdirAll() with our own system.MkdirAll() function, which
is capable of detecting GUID volumes.

- How to verify it

To verify (on Linux; don't know the equivalent on Windows, LOL):

make TEST_FILTER=TestBuildMultiStageCopy test-integration

...
INFO: Testing against a local daemon
=== RUN   TestBuildMultiStageCopy
=== RUN   TestBuildMultiStageCopy/copy_to_root
=== RUN   TestBuildMultiStageCopy/copy_to_newdir
=== RUN   TestBuildMultiStageCopy/copy_to_newdir_nested
=== RUN   TestBuildMultiStageCopy/copy_to_existingdir
=== RUN   TestBuildMultiStageCopy/copy_to_newsubdir
--- PASS: TestBuildMultiStageCopy (11.32s)
    --- PASS: TestBuildMultiStageCopy/copy_to_root (5.76s)
    --- PASS: TestBuildMultiStageCopy/copy_to_newdir (1.33s)
    --- PASS: TestBuildMultiStageCopy/copy_to_newdir_nested (1.41s)
    --- PASS: TestBuildMultiStageCopy/copy_to_existingdir (1.34s)
    --- PASS: TestBuildMultiStageCopy/copy_to_newsubdir (1.48s)
PASS
...

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

@ddebroy @StefanScherer @kolyshkin ptal

[thaJeztah]

Ah, failing, because #313 isn't merged yet

[thaJeztah]

#313 was merged; rebased this PR (should go green now)

[andrewhsu]

LGTM

[kolyshkin]

LGTM