Switching off/on separate tests in mysql-test-run suite

Now we can switch off whole test files, but usually each test file contain a lot of tests.

We have most modern tests which starts with

--echo #

--echo # MDEV-...

...

which result in

#

# MDEV-...

...

so theoretically one can separate most modern test cases inside the file, and so can theoretically switch the separate test (or only part of the file) on and off by pre-processing the test file and result file before execution.

As setup we can use the same format as now but with MDEV list and comments why they are switched off.

Possible implementation

Make `case` test command, following with the curly-braced block, e.g.:

case (MDEV-21271) Switching off/on separate tests in mysql-test-run suite

{

 # Test case code follows

}

Now it can be possible to recognize the case. We can make a switch like

--ignore-case=MDEV-21271,...