Install virtualenv in Python distribtest Dockerfiles

tools/dockerfile/distribtest/python_arch_x64/Dockerfile

@@ -33,4 +33,4 @@ RUN pacman --noconfirm -Syy
 RUN pacman --noconfirm -S openssl
 RUN pacman --noconfirm -S python2
 RUN pacman --noconfirm -S python2-pip
-
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_centos6_x64/Dockerfile

@@ -44,3 +44,5 @@ RUN curl https://bootstrap.pypa.io/get-pip.py | python -
 
 # "which" command required by python's run_distrib_test.sh
 RUN yum install -y which
+
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_centos7_x64/Dockerfile

@@ -32,4 +32,4 @@ FROM centos:7
 RUN yum install -y python
 RUN yum install -y epel-release
 RUN yum install -y python-pip
-
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_fedora20_x64/Dockerfile

@@ -35,3 +35,5 @@ RUN yum clean all && yum update -y && yum install -y python python-pip
 # Trying twice makes it work fine.
 # https://github.com/docker/docker/issues/10180
 RUN pip install --upgrade six || pip install --upgrade six
+
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_fedora21_x64/Dockerfile

@@ -40,3 +40,5 @@ RUN yum clean all && yum update -y && yum install -y python python-pip
 # Trying twice makes it work fine.
 # https://github.com/docker/docker/issues/10180
 RUN pip2 install --upgrade six || pip2 install --upgrade six
+
+RUN pip2 install virtualenv

tools/dockerfile/distribtest/python_fedora22_x64/Dockerfile

@@ -30,3 +30,4 @@
 FROM fedora:22
 
 RUN yum clean all && yum update -y && yum install -y python python-pip
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_fedora23_x64/Dockerfile

@@ -30,3 +30,4 @@
 FROM fedora:23
 
 RUN yum clean all && yum update -y && yum install -y python python-pip
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_jessie_x64/Dockerfile

@@ -30,3 +30,4 @@
 FROM debian:jessie
 
 RUN apt-get update && apt-get install -y python python-pip
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_jessie_x86/Dockerfile

@@ -31,6 +31,8 @@ FROM 32bit/debian:jessie
 
 RUN apt-get update && apt-get install -y python python-pip
 
+RUN pip install virtualenv
+
 # docker is running on a 64-bit machine, so we need to
 # override "uname -m" to report i686 instead of x86_64, otherwise
 # python will choose a wrong binary package to install.

tools/dockerfile/distribtest/python_opensuse_x64/Dockerfile

@@ -38,3 +38,5 @@ RUN zypper --non-interactive install which
 # Without this, pip won't be able to connect to
 # https://pypi.python.org/simple/
 RUN zypper --non-interactive install ca-certificates-mozilla
+
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_ubuntu1204_x64/Dockerfile

@@ -30,3 +30,5 @@
 FROM ubuntu:12.04
 
 RUN apt-get update -y && apt-get install -y python python-pip
+
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_ubuntu1404_x64/Dockerfile

@@ -30,3 +30,5 @@
 FROM ubuntu:14.04
 
 RUN apt-get update -y && apt-get install -y python python-pip
+
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_ubuntu1504_x64/Dockerfile

@@ -30,3 +30,5 @@
 FROM ubuntu:15.04
 
 RUN apt-get update -y && apt-get install -y python python-pip
+
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_ubuntu1510_x64/Dockerfile

@@ -30,3 +30,5 @@
 FROM ubuntu:15.10
 
 RUN apt-get update -y && apt-get install -y python python-pip
+
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_ubuntu1604_x64/Dockerfile

@@ -30,3 +30,5 @@
 FROM ubuntu:16.04
 
 RUN apt-get update -y && apt-get install -y python python-pip
+
+RUN pip install virtualenv

tools/dockerfile/distribtest/python_wheezy_x64/Dockerfile

@@ -30,3 +30,5 @@
 FROM debian:wheezy
 
 RUN apt-get update -y && apt-get install -y python python-pip
+
+RUN pip install virtualenv