Fix broken string constant in mysqld.cc


mysql-test/mysql-test-run.sh:
  Don't enable NDB when the slave mysqld is started
  Remove the ndbcluster dir from var/ when restarting test
  Set datadir for NDB to @MYSQL_TEST_DIR/var so that ndbcluster dir is created there. Otherwise it will appear as a database in mysqld.
sql/mysqld.cc:
  The string was broken in two lines and failed to compile on some compiler.
  Remove ifdefs around OPT_NDBCLUSTER, it should always be available even when not supported.