[v0.8 backport] frontend: fix testMultiStageImplicitFrom to account for busybox changes

[thaJeztah]

backport of

• integration: fix TestSecurityModeSysfs on cgroup v2 #3269
• frontend: fix testMultiStageImplicitFrom to account for busybox changes #3436

It looks like there's some changes between busybox:1.34.0 and up; version 1.34.0 of the image did not have a /usr/bin directory (only /usr/sbin);

docker run --rm -it busybox:1.34.0 ls -al /usr/
total 12
drwxr-xr-x    3 root     root          4096 Sep 13  2021 .
drwxr-xr-x    1 root     root          4096 Dec 27 14:45 ..
drwxr-xr-x    2 daemon   daemon        4096 Sep 13  2021 sbin

But 1.34.1 and up do;

docker run --rm -it busybox:1.34.1 ls -al usr/
total 16
drwxr-xr-x    4 root     root          4096 Dec 21 18:28 .
drwxr-xr-x    1 root     root          4096 Dec 27 14:44 ..
drwxr-xr-x    2 root     root          4096 Dec 21 18:28 bin
drwxr-xr-x    2 daemon   daemon        4096 Dec 21 18:28 sbin

It's not immediately apparent what caused this change, or if it's in busybox itself, or in the official image only;
mirror/busybox@1_34_0...1_34_1

But either way, this change caused a test to fail:

sandbox.go:238: time="2022-12-27T13:45:25.294022820Z" level=debug msg="> creating 4gr5bno8rj7l3k7h9jxe3jhal [/bin/sh -c mkdir /usr/bin && echo -n foo > /usr/bin/go]" span="[golang 2/2] RUN mkdir /usr/bin && echo -n foo > /usr/bin/go"
sandbox.go:238: time="2022-12-27T13:45:25.433886983Z" level=debug msg="sandbox set key processing took 70.062631ms for container 5b4o358g2ryquk4s6ami38gqo"
sandbox.go:238: mkdir: can't create directory '/usr/bin': File exists

(cherry picked from commit 34f9898)

needs fix TestSecurityModeSysfs on cgroup v2

[crazy-max]

https://github.com/moby/buildkit/actions/runs/3788940749/jobs/6442288496#step:7:3762

=== CONT  TestIntegration/TestSecurityModeSysfs/worker=oci/secmode=insecure
    client_test.go:680: 
        	Error Trace:	client_test.go:680
        	            				run.go:171
        	Error:      	Received unexpected error:
        	            	rpc error: code = Unknown desc = executor failed running [mkdir /sys/fs/cgroup/cpuset/securitytest]: exit code: 1
        	            	github.com/moby/buildkit/util/stack.Enable
        	            		/src/util/stack/stack.go:77
        	            	github.com/moby/buildkit/util/grpcerrors.FromGRPC
        	            		/src/util/grpcerrors/grpcerrors.go:188
        	            	github.com/moby/buildkit/util/grpcerrors.UnaryClientInterceptor
        	            		/src/util/grpcerrors/intercept.go:41
        	            	google.golang.org/grpc.(*ClientConn).Invoke
        	            		/src/vendor/google.golang.org/grpc/call.go:35
        	            	github.com/moby/buildkit/api/services/control.(*controlClient).Solve
        	            		/src/api/services/control/control.pb.go:1321
        	            	github.com/moby/buildkit/client.(*Client).solve.func2
        	            		/src/client/solve.go:201
        	            	golang.org/x/sync/errgroup.(*Group).Go.func1
        	            		/src/vendor/golang.org/x/sync/errgroup/errgroup.go:57
        	            	runtime.goexit
        	            		/usr/local/go/src/runtime/asm_amd64.s:1571
        	            	failed to solve
        	            	github.com/moby/buildkit/client.(*Client).solve.func2
        	            		/src/client/solve.go:214
        	            	golang.org/x/sync/errgroup.(*Group).Go.func1
        	            		/src/vendor/golang.org/x/sync/errgroup/errgroup.go:57
        	            	runtime.goexit
        	            		/usr/local/go/src/runtime/asm_amd64.s:1571
        	Test:       	TestIntegration/TestSecurityModeSysfs/worker=oci/secmode=insecure

This branch needs 0f34fc6

Also don't think we should backport to this branch as we don't run buildkit tests on moby/20.10 anyway.

[thaJeztah]

Tried applying that patch, but looks like it still fails on something 🤔

022/12/27 18:01:06 http2: server connection error from localhost: connection error: PROTOCOL_ERROR
=== CONT  TestIntegration/TestSecurityModeSysfs/worker=oci/secmode=insecure
    client_test.go:685: 
        	Error Trace:	client_test.go:685
        	            				run.go:171
        	Error:      	Received unexpected error:
        	            	rpc error: code = Unknown desc = executor failed running [mkdir /sys/fs/cgroup/securitytest]: exit code: 1

[crazy-max]

Closing this one as we are not running BuildKit tests on Moby 20.10 branch anyway.