DO NOT MERGE: Fixed NetworkPolicyManagerServiceTest.

NetworkPolicyManagerServiceTest had many tests there were @Suppressed
because they were obsolete and harder to fix using Easymocks.

This CL replaced EasyMock by Mockito and re-enabled most tests, although
some tests were removed because:
- It's underlying logic changed too much that.
- It would be hard to mock all external entities they interact with.
- They are covered by CTS tests.

Bug: 30764608
Test: runtest --path
frameworks/base/services/tests/servicestests/src/com/android/server/NetworkPolicyManagerServiceTest.java

(cherry picked from commit I53ff86fc9b64cb058846f1aefa244771630d9e1e)

Change-Id: Ia9cdb780cb0917477b310dc38d2e39731d6a7609