Dockerfile: added apt-utils to allow apt-ftparchive to generate index for deb packages for stage3

Change-Id: Ieb8614f62d98152d16b88263fa90a1cb48c00bb2
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/Dockerfile b/Dockerfile
index 8eec007..71e649f 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -20,7 +20,7 @@
 FROM ubuntu:16.04
 RUN  apt-get update && \
   DEBIAN_FRONTEND=noninteractive apt-get --yes install git tox make python-all python3 python3-pip debhelper wget && \
-  DEBIAN_FRONTEND=noninteractive apt-get --yes install python3-all libssl-dev flake8 && \
+  DEBIAN_FRONTEND=noninteractive apt-get --yes install python3-all libssl-dev flake8 apt-utils && \
   DEBIAN_FRONTEND=noninteractive pip3 install -U setuptools setuptools-version-command stdeb
 
 # FROM ubuntu:16.04