client/windows integration tests: plumbing work for running on windows #1944

Job	Run time
prepare	1s
test / prepare	2m 14s
test / run (containerd, ./frontend/dockerfile, integration)	2m 15s
test / run (containerd, ./frontend/dockerfile, dockerfile)	2m 13s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	2m 12s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	2m 14s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	2m 13s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	2m 13s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	2m 13s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	2m 12s
test / run (oci, ./frontend/dockerfile, integration)	2m 15s
test / run (oci, ./frontend/dockerfile, dockerfile)	2m 10s
test / run (oci-rootless, ./frontend/dockerfile, integration)	2m 13s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	2m 17s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	2m 16s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	2m 12s
image	1s
release	1s
	33m 25s

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