qmlpuppet: Point it to deployed Qt plugins as well.

With Qt5 qmlpuppet needs to find a platform plugin.

Task-number: QTCREATORBUG-8447
Change-Id: I701d17da7f68dfcdfaeda171e2421488462692eb
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>

dist/installer/mac/qmlpuppet_qt.conf

 [Paths]
 Imports = ../..
+Plugins = ../../../PlugIns