Move from mocker -> mock (python 3 transition)

[Joshua Harlow]

It appears that mock is the mocking library going forward in python so it will likely be useful to transition from mocker (used in cloud-init) to mock so that cloud-init is more future compatible. https://pypi.python.org/pypi/mock exists for python2.5+ so it seems like if we transition then it will be less painful later.

[Scott Moser (smoser)]

woudl be nice to move a lot of our tests to more consistently using a single mock/patch interface.

[Dan Watkins (oddbloke)]

I've pushed up an example of what replacing mocker with mock might look like, check the diff out at http://bazaar.launchpad.net/~daniel-thewatkins/cloud-init/replace-mocker/revision/1013?start_revid=1013 or the full file at http://bazaar.launchpad.net/~daniel-thewatkins/cloud-init/replace-mocker/view/head:/tests/unittests/test_distros/test_netconfig.py

This is only a POC as (amongst other things) I haven't updated requirements to include mock.

[Michael Vogt (mvo)]

I also pushed some code to lp:~mvo/cloud-init/py2-3 but there is a lot of work todo.

[James Falcon (falcojr)]

mock is now used everywhere

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/2418