Remove circular dependency in testlib logging code

Remove circular dependency in testlib logging code

Pass the output file name from the QTestLog to the test logger when
commencing logging rather than having the logger call back into the
QTestLog.

Change-Id: Id484635f9fcfca08a66c92f3442887e9473b6f9b
Reviewed-on: http://codereview.qt.nokia.com/3454
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>