Move preference tests over from external/apache-harmony.

Also fixes all remaining failures. Most of them were
due to us not setting "user.dir" and "user.home" correctly.
Android has traditionally left those values blank. To fix
these tests, we need to change the default prefs factory
to one rooted at a temporary directory.

Note that this change attempts the minimal possible cleanup
(mainly style, commented code formatting etc.) to these files.

bug: 13881847
Change-Id: I1918ee9af07be9612a7da142b3e584aabc860085