Fix packaged qml2puppet

The qml2puppet.pro that is located in share/qtcreator is *only* meant to
be used from a Qt Creator *build* directory.
To build a qml2puppet from a Qt Creator source directory, it must be
src/tools/qml2puppet/qml2puppet

Task-number: QTBUG-37939
Change-Id: I06a035a0a6b4a1d145c4c8f3014757cb6e104040
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>