bump containers/image to v5.0.0, buildah to v1.11.4

Move to containers/image v5 and containers/buildah to v1.11.4.

Replace an equality check with a type assertion when checking for a
docker.ErrUnauthorizedForCredentials in `podman login`.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

vendor/github.com/containers/image/v5/pkg/strslice/README.md

@@ -0,0 +1 @@
+This package was replicated from [github.com/docker/docker v17.04.0-ce](https://github.com/docker/docker/tree/v17.04.0-ce/api/types/strslice).

vendor/github.com/containers/image/v5/pkg/strslice/strslice.go

@@ -0,0 +1,30 @@
+package strslice
+
+import "encoding/json"
+
+// StrSlice represents a string or an array of strings.
+// We need to override the json decoder to accept both options.
+type StrSlice []string
+
+// UnmarshalJSON decodes the byte slice whether it's a string or an array of
+// strings. This method is needed to implement json.Unmarshaler.
+func (e *StrSlice) UnmarshalJSON(b []byte) error {
+	if len(b) == 0 {
+		// With no input, we preserve the existing value by returning nil and
+		// leaving the target alone. This allows defining default values for
+		// the type.
+		return nil
+	}
+
+	p := make([]string, 0, 1)
+	if err := json.Unmarshal(b, &p); err != nil {
+		var s string
+		if err := json.Unmarshal(b, &s); err != nil {
+			return err
+		}
+		p = append(p, s)
+	}
+
+	*e = p
+	return nil
+}