Use unittest.mock instead of third party mock
Use unittest.mock instead of third party mock

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: I2b8d8d6cf4ac29dc58cd8fe418d613445d65c3be
Signed-off-by: Sean McGinnis <961eeb09b6d45516665e15b82e013282c4faf575@gmail.com>

openstack/futurist