unattended-upgrades can block charm actions and hooks

I was just trying to perform upgrades on a unit and found that dpkg was locked by unattended-upgrades. This could be problematic to maintenance actions and hook execution.

I hopped onto the unit and found:

2017-03-30 02:09:25 INFO juju-log Installing ['ubuntu-cloud-keyring'] with options: ['--option=Dpkg::Options::=--force-confold']
2017-03-30 02:09:25 INFO install E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
2017-03-30 02:09:25 INFO install E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?
2017-03-30 02:09:25 INFO juju-log Couldn't acquire DPKG lock. Will retry in 10 seconds.
2017-03-30 02:09:35 INFO install E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
2017-03-30 02:09:35 INFO install E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?
2017-03-30 02:09:35 INFO juju-log Couldn't acquire DPKG lock. Will retry in 10 seconds.
2017-03-30 02:09:45 INFO install E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
2017-03-30 02:09:45 INFO install E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?
2017-03-30 02:09:45 INFO juju-log Couldn't acquire DPKG lock. Will retry in 10 seconds.

ubuntu@node-moingo:/var/log/juju$ ps aux | grep apt
root 33859 0.0 0.0 1884 1124 ? Ss 02:08 0:00 /bin/sh /usr/lib/apt/apt.systemd.daily
root 35377 22.3 0.0 24180 21652 pts/4 Ss+ 02:09 0:02 /usr/bin/dpkg --status-fd 10 --unpack --auto-deconfigure /var/cache/apt/archives/linux-image-4.4.0-71-generic_4.4.0-71.92_arm64.deb /var/cache/apt/archives/linux-generic_4.4.0.71.77_arm64.deb /var/cache/apt/archives/linux-image-generic_4.4.0.71.77_arm64.deb /var/cache/apt/archives/linux-headers-4.4.0-71_4.4.0-71.92_all.deb /var/cache/apt/archives/linux-headers-4.4.0-71-generic_4.4.0-71.92_arm64.deb /var/cache/apt/archives/linux-headers-generic_4.4.0.71.77_arm64.deb /var/cache/apt/archives/linux-libc-dev_4.4.0-71.92_arm64.deb
root 35387 0.0 0.0 4100 600 pts/4 S+ 02:09 0:00 dpkg-deb --fsys-tarfile /var/cache/apt/archives/linux-image-4.4.0-71-generic_4.4.0-71.92_arm64.deb
root 35388 1.0 0.0 4100 128 pts/4 S+ 02:09 0:00 dpkg-deb --fsys-tarfile /var/cache/apt/archives/linux-image-4.4.0-71-generic_4.4.0-71.92_arm64.deb
root 35389 99.4 0.0 7616 4880 pts/4 R+ 02:09 0:08 dpkg-deb --fsys-tarfile /var/cache/apt/archives/linux-image-4.4.0-71-generic_4.4.0-71.92_arm64.deb
ubuntu 35439 0.0 0.0 4280 592 pts/3 S+ 02:09 0:00 grep --color=auto apt