Invalid cmake variable in mysql-test/CMakeLists.txt

There's a typo (invalid cmake variable syntax) inside mysql-test/CMakeLists.txt:

< --skip-rpl --skip-ndbcluster $(EXP))
> --skip-rpl --skip-ndbcluster ${EXP})

It's line 97 in 5.5.34 tarball and line 77 of current 5.5 HEAD (I just checked http://bazaar.launchpad.net/~maria-captains/maria/5.5/view/head:/mysql-test/CMakeLists.txt).

It causes ninja build to fail if test and EMBEDED_SERVER is enabled.