new "image" mount type

Add a new "image" mount type to `--mount`.  The source of the mount is
the name or ID of an image.  The destination is the path inside the
container.  Image mounts further support an optional `rw,readwrite`
parameter which if set to "true" will yield the mount writable inside
the container.  Note that no changes are propagated to the image mount
on the host (which in any case is read only).

Mounts are overlay mounts.  To support read-only overlay mounts, vendor
a non-release version of Buildah.

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

vendor/github.com/fsouza/go-dockerclient/container_copy.go

@@ -0,0 +1,49 @@
+package docker
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+)
+
+// CopyFromContainerOptions contains the set of options used for copying
+// files from a container.
+//
+// Deprecated: Use DownloadFromContainerOptions and DownloadFromContainer instead.
+type CopyFromContainerOptions struct {
+	OutputStream io.Writer `json:"-"`
+	Container    string    `json:"-"`
+	Resource     string
+	Context      context.Context `json:"-"`
+}
+
+// CopyFromContainer copies files from a container.
+//
+// Deprecated: Use DownloadFromContainer and DownloadFromContainer instead.
+func (c *Client) CopyFromContainer(opts CopyFromContainerOptions) error {
+	if opts.Container == "" {
+		return &NoSuchContainer{ID: opts.Container}
+	}
+	if c.serverAPIVersion == nil {
+		c.checkAPIVersion()
+	}
+	if c.serverAPIVersion != nil && c.serverAPIVersion.GreaterThanOrEqualTo(apiVersion124) {
+		return errors.New("go-dockerclient: CopyFromContainer is no longer available in Docker >= 1.12, use DownloadFromContainer instead")
+	}
+	url := fmt.Sprintf("/containers/%s/copy", opts.Container)
+	resp, err := c.do(http.MethodPost, url, doOptions{
+		data:    opts,
+		context: opts.Context,
+	})
+	if err != nil {
+		if e, ok := err.(*Error); ok && e.Status == http.StatusNotFound {
+			return &NoSuchContainer{ID: opts.Container}
+		}
+		return err
+	}
+	defer resp.Body.Close()
+	_, err = io.Copy(opts.OutputStream, resp.Body)
+	return err
+}