avoid problems with Dialog and curses wizards during build

Dockerfile

@@ -1,6 +1,9 @@
 FROM ubuntu:xenial
 MAINTAINER Andrey Arapov <andrey.arapov@nixaid.com>
 
+# To avoid problems with Dialog and curses wizards
+ENV DEBIAN_FRONTEND noninteractive
+
 RUN apt-get update && \
     apt-get -y install python3 virtualenv mpv paxctl && \
     apt-get clean all