CI device tests

[Christopher James Halse Rogers]

So, I think the cause of much of the heartache in the packaging in
https://code.launchpad.net/~mir-team/mir/libmircommon/+merge/226704
is because the CI test is using our tools in a way that doesn't match 
standard practice.

The Breaks/Replaces pair *should* work, using apt to install those 
packages will correctly remove mircommon-dev and replace it with 
libmircommon-dev. This is not implemented in the dpkg layer, though, so 
when the device test calls dpkg --install $ALL_THE_THINGS this handling 
is not done.

It would probably be fixed by the test passing --auto-deconfigure to 
dpkg, or (better) creating a repository apt can pull from and using apt.