Update Fedora and CentOS docker images.

- Reduce image size by skipping weak package references.
- Consolidate and sort packages to install.
- Improve consistency between versions.
- Combine yum/dnf install and clean to avoid unwanted caching.
- Don't update existing packages from base image unnecessarily.

test/utils/docker/centos6/Dockerfile

@@ -1,48 +1,49 @@
-# Latest version of centos
 FROM centos:centos6
-RUN yum -y update; yum clean all;
-RUN yum -y install \
+
+RUN yum clean all && \
+    yum -y install epel-release && \
+    yum -y install \
     acl \
     asciidoc \
     bzip2 \
-    epel-release \
     file \
     gcc \
     git \
     make \
     mercurial \
     mysql \
-    mysql-server \
     MySQL-python \
-    rpm-build \
-    rubygems \
-    sed \
-    subversion \
-    sudo \
-    unzip \
+    mysql-server \
     openssh-clients \
     openssh-server \
-    which \
-    zip
-RUN yum -y install \
-    PyYAML \
     python-coverage \
     python-devel \
     python-httplib2 \
-    python-jinja2 \
     python-keyczar \
     python-mock \
     python-nose \
     python-paramiko \
     python-pip \
     python-setuptools \
-    python-virtualenv
-RUN pip install --upgrade jinja2
-RUN rpm -e --nodeps python-crypto; pip install pycrypto
+    python-virtualenv \
+    PyYAML \
+    rpm-build \
+    rubygems \
+    sed \
+    subversion \
+    sudo \
+    unzip \
+    which \
+    zip \
+    && \
+    yum clean all
+
+RUN rpm -e --nodeps python-crypto && pip install --upgrade jinja2 pycrypto
+
 RUN /bin/sed -i -e 's/^\(Defaults\s*requiretty\)/#--- \1/'  /etc/sudoers
 RUN mkdir /etc/ansible/
 RUN /bin/echo -e '[local]\nlocalhost ansible_connection=local' > /etc/ansible/hosts
-#VOLUME /sys/fs/cgroup /run /tmp
+VOLUME /sys/fs/cgroup /run /tmp
 RUN ssh-keygen -q -t rsa1 -N '' -f /etc/ssh/ssh_host_key && \
     ssh-keygen -q -t dsa -N '' -f /etc/ssh/ssh_host_dsa_key && \
     ssh-keygen -q -t rsa -N '' -f /etc/ssh/ssh_host_rsa_key && \