Tested with the standalone controller.
Without this patch, the daemon fails to build an image:
ERRO[0008] /control.Control/Solve returned error: Lockfiles must be
given as absolute path names
error creating lockfile
.buildstate/content/ingest/b8bc9e0954dc1413b6ffd69c106a1d8967130398f50626b5c5a098c5149b0bf3/lock
github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/content.(*store).ingestPaths
/home/suda/gopath/src/github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/content/store.go:369
github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/content.(*store).Writer
/home/suda/gopath/src/github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/content/store.go:233
github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/remotes.fetch
/home/suda/gopath/src/github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/remotes/handlers.go:60
github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/remotes.FetchHandler.func1
/home/suda/gopath/src/github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/remotes/handlers.go:50
github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/images.HandlerFunc.Handle
/home/suda/gopath/src/github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/images/handlers.go:33
github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/images.Handlers.func1
/home/suda/gopath/src/github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/images/handlers.go:43
github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/images.HandlerFunc.Handle
/home/suda/gopath/src/github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/images/handlers.go:33
github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/images.Dispatch.func1
/home/suda/gopath/src/github.com/tonistiigi/buildkit_poc/vendor/github.com/containerd/containerd/images/handlers.go:103
github.com/tonistiigi/buildkit_poc/vendor/golang.org/x/sync/errgroup.(*Group).Go.func1
/home/suda/gopath/src/github.com/tonistiigi/buildkit_poc/vendor/golang.org/x/sync/errgroup/errgroup.go:58
runtime.goexit
/usr/local/go/src/runtime/asm_amd64.s:2197
Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>