QmlProfiler: Show 'retry' message box when connect fails

Show the same message box as in the debugger if connecting to
the port fails.

Change-Id: I5f101fa6e7fc6166ad37c88d046aafca24a4276f
Reviewed-on: http://codereview.qt-project.org/4891


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Aurindam Jana <aurindam.jana@nokia.com>