Remain compatible with newer versions of flatpak

Newer versions of flatpak introduced a limit of the size of app
icons. Also perform a force-clean when building via the webservice
for consistency with the local build.

Change-Id: I508feb49f9f59c67214065515b5b1026a42f0aed
Signed-off-by: Mat Booth <mat.booth@redhat.com>
2 files changed