Initial pre-checks for P_S for pt-stalk

[Sveta Smirnova]

In order to add Performance Schema support to pt-stalk, check following and turn ON corresponding collections.

1. Check if Performance Schema is ON:
5.5-5.6: select variable_value from information_schema.global_variables where variable_name='performance_schema';
5.7+: select variable_value from performance_schema.global_variables where variable_name='performance_schema';
2 .Check P_S options:
5.5-5.6: select * from information_schema.global_variables where variable_name like 'performance_schema%';
5.7+: select * from performance_schema.global_variables where variable_name like 'performance_schema%';
3. Check status:
5.5-5.6: select * from information_schema.global_status where variable_name like 'performance_schema%';
5.7+: select * from performance_schema.global_status where variable_name like 'performance_schema%';
4. Check which consumers are ON:
select * from performance_schema.setup_consumers;
5. Check which instruments are ON:
select * from performance_schema.setup_instruments;
6. Check if sys schema installed:
select 1 from information_schema.schemata where schema_name='sys';

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PT-1393