mysql-test/mysql-test-run.sh : Add option "--with-ndbcluster-only" (backport from 5.1)
mysql-test/mysql-test-run.sh:
Manual merge from 4.0 (which was a 5.1 backport):
"--with-ndbcluster" is already present,
"--with-ndbcluster-only" is really usable here.