Instead of waiting a long time, let's just check that networking truly
is disabled, in the same way we do for the MAC spoofing tests -- after
all the code for the "Diable networking" feature actually originates
from the MAC spoofing feature. This way we do not have to introduce a
static wait for 120 seconds, and we do not need the anti-test.

In Jessie, org.gnome.gnome-screenshot.auto-save-directory is empty
since the default is sensible, ~/Pictures. To save the removed
scenario we'd have to set it explicitly, which seems stupid. Besides,
the 'A screenshot is taken when the PRINTSCREEN key is pressed'
scenario is already testing that GNOME Screenshot saves into this
directory, which is enough.

We want to change the owner of the symlink, not the file it points
to. Yes, this made the secret leak every time. :)

I.e. as amnesia, which doesn't have it in its PATH, and must use
sudo. This shouldn't be needed, but is more realistic if we switch the
approach later.

... and pave the way for adding more options than the user to execute
the command as.

Waiting for a random amount of time just seems like it could cause us
to miss phone-home type traffic.

Will-fix: #9402

That is, instead of sharing folders we do not necessarily own and that
may have bad permissions, we create the share source in the temporary
directory and copy/generate the necessart files there instead.

"Persistent" in the sense that it survives across scenarios. This is a
first step towards using a single Libvirt::Domain instance across the
full test suite run, which in turn is a step towards being able to use
Libvirt snapshots more easily (or at all, I think).

This was achieved with the following command:

    sed -i 's/@vm\>/$vm/g' -- features/step_definitions/*.rb \
                              features/support/*.rb \
                              features/support/helpers/*.rb

Perhaps we'll at some point want to test the same PDF later using the
GUI, then it feels safer that we've cleaned up like this.

It has no side-effects, and we don't capture stdout or check the exit
status. Later we'll --check it any way, so no need to --display the
actual dirty metadata.

Screenshots are now handled by GNOME Shell.

Will-fix: 8951

Make sure the condition we're looking for is not verified before the action that's supposed to make it true.