Dockerfile and dpkg command
Not the most elegant but:
# continue executing even if command fails
RUN dpkg -i vufind_3.1.1.deb || true
With apt version 1.1~exp11 (which is available since Ubuntu 16.04), you are able to install .deb files and resolve dependencies directly with apt
alone:
apt install ./vufind_3.1.1.deb
Mind the ./
!