debian: install dialog package
debian: install dialog package

Without the dialog package is not possible
to properly use an interactive frontend.

debconf will print the following errors:

debconf: unable to initialize frontend: Dialog
debconf: (No usable dialog-like program is installed,
so the dialog based frontend cannot be used. at
/usr/share/perl5/Debconf/FrontEnd/Dialog.pm line 76, <> line 1.)

Change-Id: I0c7142f717cacf7437dbac1e1696f39b00cb4c49

openstack/diskimage-builder,openstack/diskimage-builder,switch-ch/diskimage-builder,switch-ch/diskimage-builder