circleci/Dockerfile-qt4: Speed up package install and optimize image size

CMake/CircleCI/Dockerfile-qt4

@@ -1,8 +1,12 @@
 FROM thewtex/opengl:v0.1.0
 MAINTAINER Insight Software Consortium <community@itk.org>
 
+RUN REPO=http://cdn-fastly.deb.debian.org && \
+  echo "deb $REPO/debian jessie main\ndeb $REPO/debian jessie-updates main\ndeb $REPO/debian-security jessie/updates main" > /etc/apt/sources.list
+
 RUN apt-get update && apt-get install -y \
   qt4-dev-tools \
-  cmake
+  cmake \
+  && rm -rf /var/lib/apt/lists/*
 
 ENV APP "sudo chown -R user.user /usr/src/ && /usr/src/CTK/CMake/CircleCI/test.sh -DCTK_QT_VERSION:STRING=4"