Escalate privileges to test single user installation

tests/dockerfiles/ubuntu16/Dockerfile

@@ -1,7 +1,5 @@
 FROM ubuntu:16.04
 
-RUN useradd -ms /bin/bash user
-
 RUN apt-get update && \
     apt-get install -y \
 			curl \
@@ -9,4 +7,7 @@ RUN apt-get update && \
 			sudo \
 		&& rm -rf /var/lib/apt/lists/*
 
+RUN useradd -ms /bin/bash user \
+		&& echo 'user ALL=(ALL) NOPASSWD: ALL' >> /etc/sudoers
+
 CMD ["/sbin/init"]