support multi-image (docker) archives

Support loading and saving tarballs with more than one image.
Add a new `/libpod/images/export` endpoint to the rest API to
allow for exporting/saving multiple images into an archive.

Note that a non-release version of containers/image is vendored.
A release version must be vendored before cutting a new Podman
release.  We force the containers/image version via a replace in
the go.mod file; this way go won't try to match the versions.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

vendor/github.com/containers/common/pkg/seccomp/validate.go

@@ -0,0 +1,29 @@
+// +build seccomp
+
+package seccomp
+
+import (
+	"encoding/json"
+
+	"github.com/pkg/errors"
+)
+
+// ValidateProfile does a basic validation for the provided seccomp profile
+// string.
+func ValidateProfile(content string) error {
+	profile := &Seccomp{}
+	if err := json.Unmarshal([]byte(content), &profile); err != nil {
+		return errors.Wrap(err, "decoding seccomp profile")
+	}
+
+	spec, err := setupSeccomp(profile, nil)
+	if err != nil {
+		return errors.Wrap(err, "create seccomp spec")
+	}
+
+	if _, err := BuildFilter(spec); err != nil {
+		return errors.Wrap(err, "build seccomp filter")
+	}
+
+	return nil
+}