* PT-2141 Fix tests for pt-archiver
Fixed tests t/pt-archiver/bulk_insert.t, t/pt-archiver/issue_1225.t, t/pt-archiver/issue_1229.t
Their failures were due to change of utf8 alias from utf8mb3 in MySQL 5.7 to utf8mb4 in MySQL 8.0.
And also due to character set match check between connection ad source table.
* PT-2141 Fix tests for pt-archiver
Removed test for PT-1898, because it was broken from the beginning:
- it called pt-online-schema-change instead of pt-archiver
- it announced it will run 6 tests while was running only 2
- the test case itself did not test the issue, described in PT-1898