Tests do not properly log failures

[simon-ess]

The tests in caPutJsonLogTest.cpp are typically of the form

    testOk(!epicsStrCaseCmp(hostname, jsonParser.host.c_str()),
            "%s - %s", testPrefix, "Hostname check");

which has the problem that the output is something like

not ok 129 - DBF_ENUM test - Hostname check

which doesn't tell you exactly how they failed. This would probably be a lot nicer if they showed the issue, and even better if they only logged the issue if the test fails (though that may be too much to ask for).

(See runs on #39)

[ralphlange]

Fixed by means of #42.