Change C3P0 defaults for idle_test_period

We currently ship Confluence with a default idle_test_period of 100 seconds, and a timeout of 30 seconds:

 <property name="hibernate.c3p0.idle_test_period">100</property>
 <property name="hibernate.c3p0.max_size">30</property>
 <property name="hibernate.c3p0.max_statements">0</property>
 <property name="hibernate.c3p0.min_size">0</property>
 <property name="hibernate.c3p0.timeout">30</property>

However, it seems that setting idle_test_period greater than the timeout means that idle connections will never be tested, since idle connections will be removed from the pool after 30 seconds. And we don't set the validate property, which defaults to false, and so idle connections will never be checked with these defaults in place.

It seems that the timeout should be given a much higher value (i.e., more than 30 seconds), and idle_test_period a value lower than that, so that connections will be checked.