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 galera_sst_mysqldump often fails with error "2013: Lost connection
to MySQL server during query". The connection is lost after the test
restart one of the nodes. This happens because the server closes client
connections if it is joining a cluster through SST method mysqldump.
On unlucky runs of the test it is possible that mysqld is restarted,
and then mtr client is disconnected while it tries to determine if
galera is ready before going on with the test.
This patch rewrites galera_wait_ready.inc so that it is immune to
being disconnected.
