MB-26126: HashTableTest: Move stats tests to own class
MB-26126: HashTableTest: Move stats tests to own class

Move the testcases in HashTableTest which test various HashTable
statistics to their own test fixture HashTableStatsTest; genericising
the setup / teardown code. This is in prepation for extending these
tests to catch the issue in the linked MB.

Change-Id: I2bcd29cde51e98fa44b1e585070a2cf5bae36e7c
Reviewed-on: http://review.couchbase.org/83634
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Manu Dhundi <158873d90a7ef40f3637a222b7329c09d0222554@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine