Reset container prior to running PurgeAction
While this works in development environments without squid, once it is enabled
the TitleSquidURLs hook will end up calling the container and initializing the
memcache services. With the new Pimple 2.x that is an exception and needs to
be handled. I don't have any good way to rearrange or adjust the hook, so
instead we are going to use Container::reset() to go back to the initial state.
This also means the PurgeAction was not complete before, storage.workflow would
hold onto the old memcache and the other storage implementations receive
the memcached that PurgeAction was putting in place.