CBQE-1979: delete all content in data folder and data folder itself

Change-Id: I604646d01c78752f858796fbc468d67385186aea
Reviewed-on: http://review.couchbase.org/33237
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>