XmlRpcServletTest: ensure a new Hibernate session is used in each test

(cherry picked from commit 4f77c0c353156e6370b3023af71c780bbbbe3b8a)
Don't commit when XMLRPCExceptions are thrown

Avoid COMMITTing the current Hibernate transaction if an uncaught
Exception is thrown.

Reproducible by trying to call the following snippet via XMLRPC:

    public void testExceptionHandling() {
        TinyUrl tu = CommonFactory.createTinyUrl(TestUtils.randomString(), new Date());
        CommonFactory.saveTinyUrl(tu);
        throw new XmlRpcException("boom");
    }

(a new row will be saved in rhnTinyUrl)

(cherry picked from commit c977f322e87ee459024b43197daf29bbef996baa)