Stage3 Image Library

This represents the stage3 implementation for the image library.  At this point, we
are moving the image-centric functions to pkg/image including migration of args and
object-oriented references.  This is a not a one-for-one migration of funcs and some
funcs will need to continue to reside in runtime_img as they are overly specific to
libpod and probably not useful to others.

Signed-off-by: baude <bbaude@redhat.com>

Closes: #484
Approved by: baude

pkg/util/utils.go

@@ -44,3 +44,13 @@ func ParseRegistryCreds(creds string) (*types.DockerAuthConfig, error) {
 		Password: password,
 	}, nil
 }
+
+// StringInSlice determines if a string is in a string slice, returns bool
+func StringInSlice(s string, sl []string) bool {
+	for _, i := range sl {
+		if i == s {
+			return true
+		}
+	}
+	return false
+}