Fix unittest for the rapi client library

Wrong escape, so we make sure to use proper escapes (we want the
backslashes to be embedded, not interpreted). Also change " to ' to be
easier to read.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: David Knowles <dknowles@google.com>