Include Percona Toolkit into integration test

[adangel]

Goals:

• Make the integration test independent of a locally installed Percona Toolkit
• Have a integration test with a specific version of the toolkit, to test backwards compatibility. Note: The plan is to support always the latest toolkit - so, as soon the integration test with the latest toolkit works, the extension will be updated to support only this. This makes sense, since the toolkit usually contains important bug fixes that prevent data loss.
• Have a integration test with the latest version of the toolkit, so that problems like Unique key constraint cannot be added #15 can be detected earlier. Like a canary.