Show SELinux label on failure

We are seeing EINVAL errors with container engines setting SELinux
labels. It would be helpful to see what Labels the engines are trying
to set.

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

go-selinux/selinux_linux.go

@@ -329,7 +329,7 @@ func lSetFileLabel(fpath string, label string) error {
 			break
 		}
 		if err != unix.EINTR {
-			return &os.PathError{Op: "lsetxattr", Path: fpath, Err: err}
+			return &os.PathError{Op: "lsetxattr", Path: fpath, Err: fmt.Errorf("label=%s: %v", label, err)}
 		}
 	}
 
@@ -348,7 +348,7 @@ func setFileLabel(fpath string, label string) error {
 			break
 		}
 		if err != unix.EINTR {
-			return &os.PathError{Op: "setxattr", Path: fpath, Err: err}
+			return &os.PathError{Op: "setxattr", Path: fpath, Err: fmt.Errorf("label=%s: %v", label, err)}
 		}
 	}