tahoe: Mark Tahoe-LAFS as an advanced app

Tahoe LAFS is an app requiring some technical knowledge to use and its support
in FreedomBox is experimental. The use case of a cluster of FreedomBoxes running
Tahoe-LAFS nodes isn't tested yet. It's intended use case as a backend for the
backups app isn't implemented yet.

- Fixed functional test implementation for advanced mode
- Did not fix failing Tahoe-LAFS tests, keeping them skipped for now.

Signed-off-by: Joseph Nuthalapati <njoseph@riseup.net>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>
2 jobs for master in 13 minutes and 25 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Test
passed #404877
run-unit-tests

00:05:31

31.58%
 
  Package
passed #404878
build-debian-package

00:07:53