Add performance tests to compare crud and vshard

This patch reworks existing performance tests and adds new cases:
select for equal conditions for primary and secondary indexes
(including #220 case). It also adds corresponding vshard test cases
to compare performance. Comparison may be not exactly precise since
vshard test functions use naive mergers, but should at least estimate
basic differences.

Closes #225

test/entrypoint/srv_ddl.lua

@@ -90,6 +90,12 @@ package.preload['customers-storage'] = function()
                 },
             }
 
+            local customers_id_schema = table.deepcopy(customers_schema)
+            customers_id_schema.sharding_key = {'id'}
+            table.insert(customers_id_schema.indexes, primary_index_id)
+            table.insert(customers_id_schema.indexes, bucket_id_index)
+            table.insert(customers_id_schema.indexes, age_index)
+
             local customers_name_key_schema = table.deepcopy(customers_schema)
             customers_name_key_schema.sharding_key = {'name'}
             table.insert(customers_name_key_schema.indexes, primary_index)
@@ -133,6 +139,7 @@ package.preload['customers-storage'] = function()
 
             local schema = {
                 spaces = {
+                    customers = customers_id_schema,
                     customers_name_key = customers_name_key_schema,
                     customers_name_key_uniq_index = customers_name_key_uniq_index_schema,
                     customers_name_key_non_uniq_index = customers_name_key_non_uniq_index_schema,
@@ -166,8 +173,8 @@ local ok, err = errors.pcall('CartridgeCfgError', cartridge.cfg, {
         'customers-storage',
         'cartridge.roles.crud-router',
         'cartridge.roles.crud-storage',
-    },
-})
+    }}, { readahead = 20 * 1024 * 1024 }
+)
 
 if not ok then
     log.error('%s', err)