CBQE-0: add extra_buckets=1 in py-cbrecoverytests.conf

for cases when_step=create_bucket_when_recovery

Change-Id: Ia2f4ddb499d369be0bae284adcc954cb5609faa2
Reviewed-on: http://review.couchbase.org/36832
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>