test_flatpak_create_oci.py: Fix mock_flatpak mode for new flatpak-module-tools
test_flatpak_create_oci.py: Fix mock_flatpak mode for new flatpak-module-tools

flatpak-module-tools >= 0.10.1 calls ostree in a slightly different way.

Signed-off-by: Owen W. Taylor <ea9e9dc5381b1dcdec5e0e8197a67fa819b36a07@fishsoup.net>

projectatomic/atomic-reactor,fr34k8/atomic-reactor,DBuildService/atomic-reactor,fr34k8/atomic-reactor,projectatomic/atomic-reactor,DBuildService/atomic-reactor