Add a UIDGenerator::unitTestTearDown() method that can find an delete
cache files created by UIDGenerator. Call that cleanup method from the
tearDown() method of the UIDGenerator unit tests.
Bug: 44850
Change-Id: If342586d93bbc2a926af2dc388325dcb7c345e37
Also gets rid of some CodeSniffer errors. There are more cases in core
(cache, pool counter, installer, database, load balancer, diff, CSS
Janus, less (argh!), media, parser, revdel, ...), that have class names
with underscores I'd be trying to get rid of later.
Change-Id: I33709c05e597978a5574a445fa43c583cbd7e12b
