Copy qmldir of test import to destination directory.

Test imports, used only during tests, are not installed prior to running
tests. Copy the qmldir file to the output directory so that the tests
can successfully load the import.

Task-number: QTBUG-31797
Change-Id: I85095eb7532df6b1fc06f10e46ed8b4db41554a6
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>