Make sure qmlpuppets are installed

The qmlpuppet build steps set the destination path already in
the build steps (change 6eb9458eb). Make sure that the prefix path
is then already retrieved from qmake.

Change-Id: I3a4cc935f8e187aad54c7f820d46f44b9bc4adc3
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>