Fixed cost calculations for materialized tables

One effect of this change in the test suite is that tests with very few
rows changed to use sub queries instead of materialization. This is
correct and expected as for these the materialization overhead is too high.

A lot of tests where fixed to still use materialization by adding a
few rows to the tables (most tests has only 2-3 rows and are thus easily
affected when cost computations are changed).

Other things:
- Added more variables to TMPTABLE_COSTS for better cost calculation
- Added cost of copying rows to TMPTABLE_COSTS lookup and write
- Added THD::optimizer_cache_hit_ratio for easier cost calculations
- Added DISK_FAST_READ_SIZE to be used when calculating costs when
  reading big blocks from a disk

sql/sql_class.h

@@ -2674,6 +2674,8 @@ public:
   struct  system_status_var org_status_var; // For user statistics
   struct  system_status_var *initial_status_var; /* used by show status */
   THR_LOCK_INFO lock_info;              // Locking info of this thread
+  double optimizer_cache_hit_ratio;     // From optimizer_cache_hit_ratio
+
   /**
     Protects THD data accessed from other threads:
     - thd->query and thd->query_length (used by SHOW ENGINE