client/windows integration tests: plumbing work for running on windows #1992

Job	Run time
prepare	3s
test / prepare	1m 38s
test / run (containerd, ./frontend/dockerfile, integration)	4m 41s
test / run (containerd, ./frontend/dockerfile, dockerfile)	6m 15s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	4m 16s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	5m 29s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	4m 53s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	5m 37s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	4m 30s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	6m 11s
test / run (oci, ./frontend/dockerfile, integration)	3m 58s
test / run (oci, ./frontend/dockerfile, dockerfile)	5m 14s
test / run (oci-rootless, ./frontend/dockerfile, integration)	3m 48s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	5m 12s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	3m 59s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	4m 55s
image (mainline)	4m 41s
image (labs)	5m 8s
release	0s
	1h 20m 28s

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