PT-1860 make pt-osc respect case insesitive lookup on Windows and osx

[ikruglov]

This PR teaches pt-osc how to perform case-insensitive lookup on platform which use case insensitive filesystems, such Windows or osx. Before searching the table via SHOW TABLES FROM, pt-osc checks lower_case_table_names param and adjust it string comparison accordingly if lower_case_table_names > 0.

According to https://dev.mysql.com/doc/refman/8.0/en/identifier-case-sensitivity.html MySQL 5.6/5.7/8.0 are use case-sensitive search when lower_case_table_names == 0 and case-insensitive lookup when value is either 1 or 2.

Before the patch, pt-osc used to fail with Table does not exist error.

[it-percona-cla]

All committers have signed the CLA.

[ikruglov]

Hi @svetasmirnova. I signed CLA. Please check it out. Hope that we can merge this PR.

[percona-csalguero]

Hi @ikruglov . The PR was made with the user ikruglov-db. You need to sing the CLA with that user. Thanks