title: installing `lightdm` in Dockerfile raises interactive keyboard layout menu
body: <p>I have the following Dockerfile:</p>
  
  <pre><code># Pull from CentOS RPM Build Image
  FROM ubuntu
  
  # Update the image
  RUN apt-get update -y
  RUN apt-get install lightdm -y
  </code></pre>
  
  <p>The problem I have is when I'm building this container with <code>docker build -t dumbcontainer .</code>, at some point I get an interactive menu for choosing a keyboard layout:</p>
  
  <pre><code>Adding system user `lightdm' (UID 106) ...
  Adding new user `lightdm' (UID 106) with group `lightdm' ...
  Creating home directory `/var/lib/lightdm' ...
  usermod: no changes
  usermod: no changes
  usermod: no changes
  Adding group `nopasswdlogin' (GID 109) ...
  Done.
  Setting up libnih-dbus1:amd64 (1.0.3-4.3ubuntu1) ...
  Setting up mountall (2.54ubuntu1) ...
  Setting up perl-modules-5.22 (5.22.1-9) ...
  Setting up libperl5.22:amd64 (5.22.1-9) ...
  Setting up perl (5.22.1-9) ...
  update-alternatives: using /usr/bin/prename to provide /usr/bin/rename (rename) in auto mode
  Setting up libpython2.7-stdlib:amd64 (2.7.11-7ubuntu1) ...
  Setting up python2.7 (2.7.11-7ubuntu1) ...
  Setting up libpython-stdlib:amd64 (2.7.11-1) ...
  Setting up python (2.7.11-1) ...
  Setting up libtalloc2:amd64 (2.1.5-2) ...
  Setting up libtevent0:amd64 (0.9.28-0ubuntu0.16.04.1) ...
  Setting up libroken18-heimdal:amd64 (1.7~git20150920+dfsg-4ubuntu1) ...
  Setting up libasn1-8-heimdal:amd64 (1.7~git20150920+dfsg-4ubuntu1) ...
  Setting up libhcrypto4-heimdal:amd64 (1.7~git20150920+dfsg-4ubuntu1) ...
  Setting up libheimbase1-heimdal:amd64 (1.7~git20150920+dfsg-4ubuntu1) ...
  Setting up libwind0-heimdal:amd64 (1.7~git20150920+dfsg-4ubuntu1) ...
  Setting up libhx509-5-heimdal:amd64 (1.7~git20150920+dfsg-4ubuntu1) ...
  Setting up libkrb5-26-heimdal:amd64 (1.7~git20150920+dfsg-4ubuntu1) ...
  Setting up libheimntlm0-heimdal:amd64 (1.7~git20150920+dfsg-4ubuntu1) ...
  Setting up libgssapi3-heimdal:amd64 (1.7~git20150920+dfsg-4ubuntu1) ...
  Setting up libsasl2-modules-db:amd64 (2.1.26.dfsg1-14build1) ...
  Setting up libsasl2-2:amd64 (2.1.26.dfsg1-14build1) ...
  Setting up libldap-2.4-2:amd64 (2.4.42+dfsg-2ubuntu3.1) ...
  Setting up libtdb1:amd64 (1.3.8-2) ...
  Setting up libldb1:amd64 (2:1.1.24-1ubuntu3) ...
  Setting up libpython2.7:amd64 (2.7.11-7ubuntu1) ...
  Setting up python-talloc (2.1.5-2) ...
  Setting up samba-libs:amd64 (2:4.3.9+dfsg-0ubuntu0.16.04.2) ...
  Setting up libsmbclient:amd64 (2:4.3.9+dfsg-0ubuntu0.16.04.2) ...
  Setting up libtxc-dxtn-s2tc0:amd64 (0~git20131104-1.1) ...
  update-alternatives: using /usr/lib/x86_64-linux-gnu/libtxc_dxtn_s2tc.so.0 to provide /usr/lib/x86_64-linux-gnu/libtxc_dxtn.so (libtxc-dxtn-x86_64-linux-gnu) in auto mode
  Setting up bzip2 (1.0.6-8) ...
  Setting up distro-info-data (0.28ubuntu0.1) ...
  Setting up eject (2.1.5+deb1+cvs20081104-13.1) ...
  Setting up libmagic1:amd64 (1:5.25-2ubuntu1) ...
  Setting up file (1:5.25-2ubuntu1) ...
  Setting up iproute2 (4.3.0-1ubuntu3) ...
  Setting up ifupdown (0.8.10ubuntu1) ...
  Creating /etc/network/interfaces.
  Setting up libisc-export160 (1:9.10.3.dfsg.P4-8ubuntu1) ...
  Setting up libdns-export162 (1:9.10.3.dfsg.P4-8ubuntu1) ...
  Setting up isc-dhcp-client (4.3.3-5ubuntu12) ...
  Setting up isc-dhcp-common (4.3.3-5ubuntu12) ...
  Setting up keyboard-configuration (1.108ubuntu15) ...
  debconf: unable to initialize frontend: Dialog
  debconf: (TERM is not set, so the dialog frontend is not usable.)
  debconf: falling back to frontend: Readline
  Configuring keyboard-configuration
  ----------------------------------
  
  The layout of keyboards varies per country, with some countries having multiple
  common layouts. Please select the country of origin for the keyboard of this
  computer.
  
    1. Afghani                                     48. Irish
    2. Albanian                                    49. Italian
    3. Amharic                                     50. Japanese
    4. Arabic                                      51. Japanese (PC-98xx Series)
    5. Arabic (Morocco)                            52. Kazakh
    ........
  </code></pre>
  
  <p>I try putting an option, but the process just stalls at that point</p>
  
  <p>Is there any way that I can choose an option interactively, or have docker pass an option when asked to do so?</p>