This should make investigation of errors on testnode easiers, any logged
messages by test framework goes to testcase.log

Setup logging at the very beginning, to also have messages logged during
initialization

Also adjust a bit the logged messages, we don't need to log everytime we
snapshot a file or folder, this cause the log to be very big, but it can
be interesting to log when we start and stop checking software, so that
we see how long this took.