Revert "Make /proc/<pid>/ invisible and restricted for other users." (Closes: #8256).

This reverts commit 20a76c4083fa76f3f4e656fb8023247fa15d6a22.

hidepid != 0 in its current simplistic form can't be supported by systemd:

https://bugzilla.redhat.com/show_bug.cgi?id=1130796#c2
http://lists.freedesktop.org/archives/systemd-devel/2012-October/006860.html
Enable the native memlockd systemd unit file.
Set memlockd.service's OOMScoreAdjust to -17.

We don't want *this* service to be killed by the OOM killer.
Adjust some bits of the manual test suite for Jessie.
Don't load acpi-cpufreq at boot time.

It fails to load whenever no device it supports is present, which makes the
systemd-modules-load.service fail. Anyway, these days, the kernel should just
automatically load such modules when they are needed.

(We started loading this module five years ago, in commit e6aaca8.)
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.