OnlineTestCase support for failure on failed connection

OnlineTestCase disables an online test if connect() fails. This may not be the desired behaviour. The attached patch (for trunk) adds an optional key to the test fixture property file that allows this behaviour to be changed.

From the javadoc:

The default behaviour of this class is that if connect() throws an exception, the test
suite is disabled, causing each test to pass without being run. In addition, exceptions thrown by
disconnect() are ignored. This behaviour allows tests to be robust against transient
outages of online resources, but also means that local software failures in connect() or
disconnect() will be silent.

To have exceptions thrown by connect() and disconnect() cause tests to fail,
set skip.on.failure=false in the fixture property file. This restores the
traditional behaviour of unit tests, that is, that exceptions cause unit tests to fail.