sun.security.x509: linting and types tidying. Port from jdk8u60

Changes that don't impact behaviour like:
- Added casts
- Added SuppressWarnings annotations
- Add generics
- Remove unused imports
- Use class name instead of object name when calling static methods

This CL finishes the port of security and crypto packages from jdk8u60.
Any time in the future that I'm facing a terrible, huge task, I'll remember
this moment, hold a deep breath, and say to myself: "Sergio, you can do it."

Bug: 29631070
Test: make droid
Change-Id: I516c7a1a5c2053cce1a63016c89d5c7e74f70f48