the server's binlog file, might be set to a different directory.  This adds a new
"vardir" parameter, which takes the name of the directory as a value, so that the 
test_bug17667() test can find the binlog.  


mysql-test/mysql-test-run.pl:
  Add the "vardir" to the options passed to "mysql_test_client", so we know 
  where to find the binlog file.
tests/mysql_client_test.c:
  Receive a new option, "vardir".
  
  Use the vardir option to find the binlog file in test_bug17667() .