* Add BagOStuffTest subclasses for all core BagOStuff subclasses,
replacing PHPUNIT_USE_BAGOSTUFF, as suggested in a todo comment.
* Add config $wgEnableRemoteBagOStuffTests which causes all tests
enabled by $wgObjectCache to execute, which means that the memcached
tests are executed by default.
I have verified all except RESTBagOStuff and WinCacheBagOStuff. The
memcached tests fail against memcached 1.5.x but pass against memcached
1.6.x.
Bug: T90875
Change-Id: Id74b5226669f8cb857f859fbc35bc58ab001e873
