Consider moving the mockCgroup from runc

[rata]

In runc we use this module and have a mock that implements the cgroup interface. However, when a method is added to it (as it happened with the Stats method in release 0.0.7: dbb23b4), we need to manually sync the mock with the new method.

I'd move the mock to this repo. This way upgrades are simpler, and providing mocks for your interfaces to be tested is usually a good practice. Also, if others are using this, they will benefit.

What do you think?

[kolyshkin]

I might be very wrong here but IMHO tests in libcontainer/container_linux_test.go are not very useful yet over-complicated, and rather than moving the mockCgroupManager around between repos I'd just remove these tests (first checking that the overall test coverage won't decrease).