CBQE-0: add ?basic_stats=true in buckets api

this is a temporary solution to get basic_stats that is not available by default

Change-Id: I7cb493253a6f65cc31d38710672c9841e3ccb6bf
Reviewed-on: http://review.couchbase.org/27835
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>