This is a solution that works for the other functions that interact with
group objects, making it a better overall solution to be used widely
in win_groupadd.
This also updates the mocking in the tests such that we use a more
comprehensive fake class, and more intelligent mocking of get_sam_name
using a lambda.
Move the code that sets up the group object, computer object and gets
existing members out of the individual functions so they can be mocked
Mock the GroupObj
Mock the ComputerObj
Mock existing members
Still need to fix info, getent, and members
