CBQE-1003:get_bucket_size is not correct

https://github.com/couchbase/testrunner/commit/7719210066826b7430a5af85e21be88b9ef8f44f
before we had:
    def _get_bucket_size(self, quota, num_buckets, ratio=2.0 / 3.0):
        ip = self.servers[0]
        for server in self.servers:
	    if server.ip == ip:
 	       	  return int(ratio / float(self.num_servers) / float(num_buckets) * float(quota))
        return int(ratio / float(num_buckets) * float(quota))

condition 'if server.ip == ip' never returns True

so we never used num_servers in get_bucket_size

Change-Id: Ib0d83cf04c218adda5b1c8153a4d4dd8bb38ae2d
Reviewed-on: http://review.couchbase.org/24788
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: buildbot <build@couchbase.com>