Allow DevicePolicyController and User to be AutoClosed.

This enables an easier style of testing when you want to create a user
and remove at the end of the test - or enable a DPC and remove it at the
end of the test.

This pattern can be re-used elsewhere as new functionality is added to
Nene.

Test: atest NeneTest
Bug: 180595646
Change-Id: Iff541c0a9e62a13acaf10715b5c7feea265065fd
4 files changed