Open() autotest serial port only if not already open.

It seems like pySerial nowadays automatically opens the serial port
upon object initialization. If we try to open it any way, we get an
"already open" exception.
In Jessie, the Terminal entry has moved into Applications -> Utilities.
In Jessie, notify-send needs the DBUS_SESSION_BUS_ADDRESS used by the GNOME session.
Don't look for the "Tor is ready" notification.

In Wheezy notifications already became unreliable too look for since
they always timeout after 5 seconds. Now in Jessie we do not only have
that problem, but the notification is placed on top of GNOME's bottom
panel *and* is transparent, so any application entries there will
affect how the notification appears.

The "Tor is ready" step already makes sure that Tor works by looking
at the exact same thing that triggers the notification, so we do not
lose anything. Well, except checking that the notification works
(which it didn't until the previous commit) but we should then test
that in its own step where we for instance make sure that the bottom
panel is empty, or similar.
Lower required free (non-buffer/cache) memory for Tails Upgrader.

At least in Jessie, this value is generally around 75 MiB in the
automated test suite, preventing the upgrade check from
happening. It's been lowered to an arbitrarily chosen 32 MiB, but I
wonder if we can remove that check completely. After all, the
available memory + buffers + cache should be what actually matters.
Update a few automated test suite images for Jessie.
In Jessue, pmap doesn't show complete .so file paths by default.
In Jessie, Synaptic has moved directly into Applications -> System Tools.
Merge remote-tracking branch 'origin/feature/jessie' into test/jessie
Don't add the Live user to the non-existent 'fuse' group.

The 'fuse' group was dropped in fuse 2.9.3-5 due to Debian bug
Revert "Don't install virtualbox-guest-utils: it's been removed from Jessie."

This reverts commit 873f64ea2680036ccd891fa8d9411cd809783df7.

virtualbox-guest-utils is back in Jessie.
Revert "Disable VirtualBox guest modules building: the needed packages were removed from Jessie."

This reverts commit 506fe82a19fe0b668b96bd73de3a13c594ccdab9.

Since the needed packages are back in Jessie, we can build the modules
again.
Fix VirtualBox build for Jessie.

A modern enough gcc is available in Jessie, so we can drop the
workaround which actually breaks the build in Jessie.
Fix comment.
Enable VirtualBox guest additions by default (Closes: #5730)

Conflicts:
	config/chroot_local-hooks/50-virtualbox

This change was lost in feature/jessie in the conflict resolution of
merge dfe65a7.
Simplify.
Close pkexec prompt when we're done testing.

It doesn't close automatically after three tries, like in Wheezy, so
this is needed so we then can see the ("complete") failure message
written to the terminal.
Adapt for changed nmcli syntax and output in Jessie.
New NM connection files must be manually loaded in Jessie.
Update some more automated test suite images for Jessie.