refactor adding enum for storage types

Signed-off-by: Mike Brown <brownwm@us.ibm.com>

registry/storage/driver/storagedriver.go

@@ -116,7 +116,7 @@ type FileWriter interface {
 // number of path components separated by slashes, where each component is
 // restricted to alphanumeric characters or a period, underscore, or
 // hyphen.
-var PathRegexp = regexp.MustCompile(`^(/[A-Za-z0-9._:-]+)+$`)
+var PathRegexp = regexp.MustCompile(`^(/[A-Za-z0-9._-]+)+$`)
 
 // ErrUnsupportedMethod may be returned in the case where a StorageDriver implementation does not support an optional method.
 type ErrUnsupportedMethod struct {