(maint) Set DEBIAN_FRONTEND=noninteractive on upgrade

When upgrading Debian packages, the system sometimes what to prompt the
user about what action to perform.  Since a tasks is supposed to be
non-interactive, we should disable such prompts.

This help when updating some packages, e.g. postfix.

Author: smortex

tasks/init.rb

@@ -8,6 +8,7 @@
 def apt_get(action)
   cmd = ['apt-get', action]
   cmd << '-y' if ['upgrade', 'dist-upgrade', 'autoremove'].include?(action)
+  ENV['DEBIAN_FRONTEND'] = 'noninteractive' if ['upgrade', 'dist-upgrade'].include?(action)
   stdout, stderr, status = Open3.capture3(*cmd)
   raise Puppet::Error, stderr if status != 0
   { status: stdout.strip }