Use a factory class for dependency injection, add more tests.

- Extracting into a factory allows us to use mocks in other classes.
(Such as Owners.)

- Also removed broken test ApplicationRestrictionsTest.  Instead added a new
simplified test to DevicePolicyManagerTest.

- Also stop caching rarely used instances in DPMS.

Bug 24061108
Bug 24275172

Change-Id: Ice9e57204b18e7b5f6b115126dab2209041439c2