Fixing Index Discovery for 5.7 and removing innodb_parallel_read_threads from init sequences for MySql5.7 compliance.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 49.47%. Comparing base (235a4a3) to head (a609ca7).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1758 +/- ## ============================================ + Coverage 42.57% 49.47% +6.90% + Complexity 3357 1095 -2262 ============================================ Files 815 337 -478 Lines 47672 18209 -29463 Branches 5107 1846 -3261 ============================================ - Hits 20294 9009 -11285 + Misses 25718 8593 -17125 + Partials 1660 607 -1053 ``` | [Components](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | Coverage Δ | | |---|---|---| | [spanner-templates](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `64.66% <100.00%> (+0.14%)` | :arrow_up: | | [spanner-import-export](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `∅ <ø> (∅)` | | | [spanner-live-forward-migration](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `75.00% <ø> (ø)` | | | [spanner-live-reverse-replication](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `51.96% <ø> (ø)` | | | [spanner-bulk-migration](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `83.46% <100.00%> (+0.01%)` | :arrow_up: | | [Files](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | Coverage Δ | | |---|---|---| | [...jdbc/dialectadapter/mysql/MysqlDialectAdapter.java](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758?src=pr&el=tree&filepath=v2%2Fsourcedb-to-spanner%2Fsrc%2Fmain%2Fjava%2Fcom%2Fgoogle%2Fcloud%2Fteleport%2Fv2%2Fsource%2Freader%2Fio%2Fjdbc%2Fdialectadapter%2Fmysql%2FMysqlDialectAdapter.java&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform#diff-djIvc291cmNlZGItdG8tc3Bhbm5lci9zcmMvbWFpbi9qYXZhL2NvbS9nb29nbGUvY2xvdWQvdGVsZXBvcnQvdjIvc291cmNlL3JlYWRlci9pby9qZGJjL2RpYWxlY3RhZGFwdGVyL215c3FsL015c3FsRGlhbGVjdEFkYXB0ZXIuamF2YQ==) | `99.63% <100.00%> (+<0.01%)` | :arrow_up: | | [...iowrapper/config/defaults/MySqlConfigDefaults.java](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758?src=pr&el=tree&filepath=v2%2Fsourcedb-to-spanner%2Fsrc%2Fmain%2Fjava%2Fcom%2Fgoogle%2Fcloud%2Fteleport%2Fv2%2Fsource%2Freader%2Fio%2Fjdbc%2Fiowrapper%2Fconfig%2Fdefaults%2FMySqlConfigDefaults.java&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform#diff-djIvc291cmNlZGItdG8tc3Bhbm5lci9zcmMvbWFpbi9qYXZhL2NvbS9nb29nbGUvY2xvdWQvdGVsZXBvcnQvdjIvc291cmNlL3JlYWRlci9pby9qZGJjL2lvd3JhcHBlci9jb25maWcvZGVmYXVsdHMvTXlTcWxDb25maWdEZWZhdWx0cy5qYXZh) | `100.00% <100.00%> (ø)` | | ... and [494 files with indirect coverage changes](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1758/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform)