Add tests/test-export test script

The test-export script tests the `ade export` command.
It creates an install target in moc/Makefile.in and uses it to
simulate ade's export command, which further bundles the installed files
The script then unpacks the created bundle and verified the sample file
that was bundled through `ade export`

Currently, we do it the crude way to extract the file from the bundle
because ostree/flatpak doesn't have a cleaner implementation
For details, see: https://github.com/flatpak/flatpak/issues/126



Signed-off-by: Ritesh Raj Sarraf <ritesh.sarraf@collabora.com>
Reviewed-by: Frédéric Dalleau <frederic.dalleau@collabora.com>
Differential Revision: https://phabricator.apertis.org/D7914