gio/tests/portal-support: Fix snap test ordering race

When the gnome test runner executes the tests, the test appear to execute in disk order. This means it sometimes works and sometimes we see breakage in portal-support-snap and portal-support-snap-classic.

The issue is that some tests create config files but some don't. If they run in the wrong order, tests see config files they shouldn't and break.

Fix this by deleting the files after each test run, properly cleaning up after themselves. The cleanup code is based upon gtestutils.c:rm_rf().

Signed-off-by: Richard Purdie richard.purdie@linuxfoundation.org

Closes #3020 (closed)