ISPN-3324 JDBC cache store test suite can hang because of c3p0 bug

https://issues.jboss.org/browse/ISPN-3324

* the suite runs single threaded now. It can be switched back to multi-threaded once https://sourceforge.net/p/c3p0/bugs/119/ is fixed
* the added test execution duration is about 1 min up from 1min 30 secs