On every Ubuntu host with unattended-upgrades, get_host_status() read the
package manager as busy, so an interrupted dpkg was never reported there.
Ubuntu keeps unattended-upgrade-shutdown --wait-for-signal running all the
time; its process name is cut to 15 characters, unattended-upgr, the same
as a real run's.
BUSY_CHECK now matches dpkg, apt, apt-get and aptitude by name and
unattended-upgrade by its command line. The tests run it through sh with a
stand-in ps, and check that the command does not match itself: over an exec
channel it is the command line of the shell that runs it.
Closes#26
christianmanivong