Show c/storage (Buildah/CRI-O) containers in ps

The `podman ps --all` command will now show containers that
are under the control of other c/storage container systems and
the new `ps --storage` option will show only containers that are
in c/storage but are not controlled by libpod.

In the below examples, the '*working-container' entries were created
by Buildah.

```
podman ps -a
CONTAINER ID  IMAGE                             COMMAND  CREATED       STATUS                   PORTS  NAMES
9257ef8c786c  docker.io/library/busybox:latest  ls /etc  8 hours ago   Exited (0) 8 hours ago          gifted_jang
d302c81856da  docker.io/library/busybox:latest  buildah  30 hours ago  storage                         busybox-working-container
7a5a7b099d33  localhost/tom:latest              ls -alF  30 hours ago  Exited (0) 30 hours ago         hopeful_hellman
01d601fca090  localhost/tom:latest              ls -alf  30 hours ago  Exited (1) 30 hours ago         determined_panini
ee58f429ff26  localhost/tom:latest              buildah  33 hours ago  storage                         alpine-working-container

podman ps --external
CONTAINER ID  IMAGE                             COMMAND  CREATED       STATUS    PORTS  NAMES
d302c81856da  docker.io/library/busybox:latest  buildah  30 hours ago  external         busybox-working-container
ee58f429ff26  localhost/tom:latest              buildah  33 hours ago  external         alpine-working-container

```
Signed-off-by: TomSweeneyRedHat <tsweeney@redhat.com>
Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

2 files changed, 9 insertions, 1 deletions

diff --git a/libpod/image/image.go b/libpod/image/image.go
index 2d055cc44..3a8152ee2 100644
--- a/libpod/image/image.go
+++ b/libpod/image/image.go
@@ -466,6 +466,14 @@ func (ir *Runtime) getImage(image string) (*storage.Image, error) {
 	return img, nil
 }
 
+func (ir *Runtime) ImageNames(id string) ([]string, error) {
+	myImage, err := ir.getImage(id)
+	if err != nil {
+		return nil, errors.Wrapf(err, "error getting image %s ", id)
+	}
+	return myImage.Names, nil
+}
+
 // GetImages retrieves all images present in storage
 func (ir *Runtime) GetImages() ([]*Image, error) {
 	return ir.getImages(false)
diff --git a/libpod/image/prune.go b/libpod/image/prune.go
index 5a9ca5d8e..fcc65fb03 100644
--- a/libpod/image/prune.go
+++ b/libpod/image/prune.go
@@ -137,7 +137,7 @@ func (ir *Runtime) PruneImages(ctx context.Context, all bool, filter []string) (
 		}
 		if err := p.Remove(ctx, true); err != nil {
 			if errors.Cause(err) == storage.ErrImageUsedByContainer {
-				logrus.Warnf("Failed to prune image %s as it is in use: %v", p.ID(), err)
+				logrus.Warnf("Failed to prune image %s as it is in use: %v.\nA container associated with containers/storage i.e. Buildah, CRI-O, etc., maybe associated with this image.\nUsing the rmi command with the --force option will remove the container and image, but may cause failures for other dependent systems.", p.ID(), err)
 				continue
 			}
 			return nil, errors.Wrap(err, "failed to prune image")