CBQE-0: upgrade: do not delete path folder, but delete data

Change-Id: Iace454bdb4bb50625891a5a03d114def3c11cf95
Reviewed-on: http://review.couchbase.org/32904
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>