Disable things which may lock /var/lib/dpkg/lock

Disable things which may lock /var/lib/dpkg/lock

The ubuntu1604 verify job has been failing due
to locking of /var/lib/dpkg/lock:

https://lists.fd.io/pipermail/vpp-dev/2016-May/000992.html

This appears to only happen with the first job run against
a particular Jenkins slave, and upon using:

https://gerrit.fd.io/r/#/c/1121/

to probe it, two candidates emerge:

apt.systemd.daily

and

unattended-upgrades

So this patch removes unattended-upgrades

and

stops/disables apt.systemd.daily via systemd

Change-Id: Ic2bc9e4ec54ef1f2d0ab35813c4623a67a43f00a
Signed-off-by: Ed Warnicke <eaw@cisco.com>