Bug#58512 Performance_schema.myisam_file_io fails sporadically in PB2

Before this fix, the test myisam_file_io executed:
- (a) an update on setup_instrument to disable non myisam file io instruments
- (b) a truncate on events_waits_history_long
and later
- (c) a select on events_waits_history_long

Surprisingly, events that were supposed to be disabled in (a) and removed in (b)
still were found in (c).

This happened for events such as 
  wait/io/file/innodb/innodb_data_file fil0fil.c: sync  
because the sync was started before (a) and completed after (b),
and as a consequence was added in the performance schema history, as expected.

Presence of these records in the history made the test fail. 

This fix makes the test script more robust to account for extra spill waits records in (c).

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

@@ -16,6 +16,7 @@ operation, number_of_bytes,
 substring(object_name, locate("no_index_tab", object_name)) as short_name
 from performance_schema.events_waits_history_long
 where operation not like "tell"
+  and event_name like "wait/io/file/myisam/%"
   order by thread_id, event_id;
 event_name	short_source	operation	number_of_bytes	short_name
 wait/io/file/myisam/kfile	mi_create.c:	create	NULL	no_index_tab.MYI

mysql-test/suite/perfschema/t/myisam_file_io.test

@@ -46,6 +46,13 @@ insert into no_index_tab set a = 'foo', b = 1;
 # Verification
 # Note that mi_create.c contains mysql_file_tell() calls in debug only,
 # so the result are filtered to remove 'tell'.
+# Note that even after setting other instruments to enabled='NO'
+# and truncating the events_waits_history_long table,
+# some events -- that were already started but not completed --
+# for other instruments could still be added in the history.
+# To protect against that, an extra where clause
+# "and event_name like "wait/io/file/myisam/%"
+# is added to the select to filter out the result.
 
 select event_name,
   left(source, locate(":", source)) as short_source,
@@ -53,6 +60,7 @@ select event_name,
   substring(object_name, locate("no_index_tab", object_name)) as short_name
   from performance_schema.events_waits_history_long
   where operation not like "tell"
+  and event_name like "wait/io/file/myisam/%"
   order by thread_id, event_id;
 
 # In case of failures, this will tell if file io are lost.