Bug#53102 perfschema.pfs_upgrade fails on sol10 sparc64 max in parallel mode

The reason for the bug above is unclear but
- Modify pfs_upgrade so that it's result is easier to analyze in case something fails
- Fix several minor weaknesses which could cause that a successing test (either an
  already existing or a to be developed one) fails because of imperfect cleanup,
  too slow disconnected sessions etc.
should either fix the bug or reduce it's probability or at least
make the analysis of failures easier.

mysql-test/suite/perfschema/r/query_cache.result

@@ -65,3 +65,4 @@ Variable_name	Value
 Qcache_hits	1
 SET GLOBAL query_cache_size= default;
 drop table t1;
+flush status;