Even moar refactoring...

- Moved DumpstateUtil functions to its own .cpp file.
- Created a DumpstateInternal file.
- Moved properties setting to a PropertiesHelper class.
- Added title to functions that uses a FD.
- Moved Nanotime() out of DurationReporter.
- Restricted number of default CommandOptions constants.

BUG: 31982882
Test: manual verification
Test: dumpstate_test pass

Change-Id: Iab3e61594f6f7298484185f6f302472d31064f7d