Switch to Debian Stretch for building CoreOS images

It seems that Jessie is no longer supported, and its backports repo
is no longer available, hence all CoreOS jobs fail.

Also install setuptools into the environment explicitly, since some
dependencies fail to install without it.

Change-Id: I751522209d07caa26422a75b108f8c8baf782028

Dockerfile

@@ -1,4 +1,4 @@
-FROM debian:jessie
+FROM debian:stretch
 
 # The add is before the RUN to ensure we get the latest version of packages
 # Docker will cache RUN commands, but because the SHA1 of the dir will be
@@ -16,9 +16,6 @@ COPY proxy.sh /usr/bin/proxy.sh
 # Ensure we hit a single mirror for builds, since httpredir is flakey
 RUN sed -i 's/httpredir/http.us/g' /etc/apt/sources.list
 
-# Add 'backports' for qemu-utils
-RUN echo 'deb http://http.us.debian.org/debian jessie-backports main' > /etc/apt/sources.list.d/backports.list
-
 # Install requirements: Python for ironic-python-agent, others for putting an
 # image on disk
 RUN proxy.sh apt-get update && \
@@ -27,8 +24,7 @@ RUN proxy.sh apt-get update && \
         python2.7 python2.7-dev python-pip qemu-utils parted hdparm \
         util-linux genisoimage git gcc bash coreutils tgt dmidecode \
         ipmitool psmisc dosfstools bsdmainutils open-iscsi udev \
-        smartmontools iptables lshw && \
-    proxy.sh apt-get --only-upgrade -t jessie-backports install -y qemu-utils
+        smartmontools iptables lshw
 
 # Some cleanup
 RUN proxy.sh apt-get -y autoremove && \
@@ -40,7 +36,7 @@ RUN apt-mark manual python-minimal
 
 # Install requirements separately, because pip understands a git+https url
 # while setuptools doesn't
-RUN proxy.sh pip install --upgrade pip
+RUN proxy.sh pip install --upgrade pip setuptools
 RUN proxy.sh pip install -c /tmp/ironic-python-agent/upper-constraints.txt --no-cache-dir -r /tmp/ironic-python-agent/requirements.txt
 
 # This will succeed because all the dependencies were installed previously