Now that we no longer support py27, we can use the standard library
unittest.mock module instead of the third party mock lib.
Change-Id: I130c03e12ddc53ce7ced728a43b10b142f7b066f
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>
Co-Authored-By: Hiroo Kitamura <hiroo.kitamura@ntt-at.co.jp>