note that:
* unit.conc_tls is broken in mtr
* schannel now doesn't fail on invalid ca path unless
--ssl-verify-server-cert is used. openssl still does.
On Windows systems, occurrences of ERROR_SHARING_VIOLATION due to
conflicting share modes between processes accessing the same file can
result in CreateFile failures.
mysys' my_open() already incorporates a workaround by implementing
wait/retry logic on Windows.
But this does not help if files are opened using shell redirection like
mysqltest traditionally did it, i.e via
--echo exec "some text" > output_file
In such cases, it is cmd.exe, that opens the output_file, and it
won't do any sharing-violation retries.
This commit addresses the issue by introducing a new built-in command,
'write_line', in mysqltest. This new command serves as a brief alternative
to 'write_file', with a single line output, that also resolves variables
like "exec" would.
Internally, this command will use my_open(), and therefore retry-on-error
logic.
Hopefully this will eliminate the very sporadic "can't open file because
it is used by another process" error on CI.
Test fixes:
Since fix for CONC-603 (wrong error handling in TLS read/write) in case
of a read/write error client doesn't return always error 2013 (server
has gone away), so in addition we need to check for error 2026
(TLS/SSL error) and 5014 (write error).
