Revert "Dont install python-pip for py3k"

This reverts commit ab89c7d69c.

This commit checked for DIB_PYTHON_VERSION and only installed the v3
packages.  This is unfortunately backwards-incompatible, as consumers
such as the openstack gate are relying on this package installing pip
& virtualenv packages for python2 AND python3.

This was sort-of expressed in the docs, where it discusses what the
resulting setup of the system will be, but I've added a note to make
it clearer.

If we want to change this, I think we'll need either a new element, or
a non-defaulting flag.

Change-Id: I419dbdf4682394db68974944af1e5c432f3e0565

diskimage_builder/elements/pip-and-virtualenv/README.rst

@@ -4,6 +4,10 @@ pip-and-virtualenv
 
 This element installs pip and virtualenv in the image.
 
+.. note:: This element setups and Python 2 and Python 3 environment.
+          This means it will bring in python2 packages, so isn't
+          appropriate if you want a python3 only environment.
+
 Package install
 ===============
 

diskimage_builder/elements/pip-and-virtualenv/install.d/pip-and-virtualenv-source-install/04-install-pip

@@ -115,7 +115,7 @@ else
     # time and you had to use "python -m venv".  Since then virtualenv
     # has gained 3.4 support so the pip install below will work
     if [[ ${DIB_PYTHON_VERSION} == 3 ]]; then
-        packages=$(echo "$packages" | sed s/python-virtualenv/python3-virtualenv/ | sed s/python-pip/python3-pip/)
+        packages=$(echo "$packages" | sed s/python-virtualenv/python3-virtualenv/)
     fi
 
     apt-get -y install $packages
@@ -126,12 +126,9 @@ else
     # These install into /usr/local/bin so override any packages, even
     # if installed later.
 
-    if [[ ${DIB_PYTHON_VERSION} == 3 ]]; then
     python3 /tmp/get-pip.py $pip_args
-        pip3 install $pip_args virtualenv
-    else
     python2 /tmp/get-pip.py $pip_args
+
+    pip3 install $pip_args virtualenv
     pip install $pip_args virtualenv
 fi
-
-fi