Revert "Pin the pip version to 7.1.2"

This reverts commit 14dfbc13.
This issue has already been fixed after pip 8.0.1 released.

TrivialFix

Change-Id: Ie559286beac56aa5ac35addd647c1d342ba6562b

docker/kolla-ansible/Dockerfile.j2

@@ -33,15 +33,9 @@ RUN apt-get -y --no-install-recommends install \
 
 {% endif %}
 
-# TODO(jeffrey4l): Pin the pip to the 7.1.2. version. latest pip
-# (now 8.0) can not install the package when conflict with the
-# system. The best solution should use the virtualenv for
-# isolation or following bug is fixed:
-# https://github.com/pypa/pip/pull/3389
 RUN curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py \
     && python get-pip.py \
     && rm get-pip.py \
-    && pip install pip==7.1.2 \
     && pip --no-cache-dir install --upgrade wheel \
     && pip --no-cache-dir install \
         MySQL-python \

docker/openstack-base/Dockerfile.j2

@@ -105,20 +105,13 @@ RUN apt-get install -y --no-install-recommends \
     {% endif %}
 
 ADD openstack-base-archive /openstack-base-source
-# TODO(jeffrey4l): Pin the pip to the 7.1.2. version. latest pip
-# (now 8.0) can not install the package when conflict with the
-# system. The best solution should use the virtualenv for
-# isolation or following bug is fixed:
-# https://github.com/pypa/pip/pull/3389
 RUN ln -s openstack-base-source/* /requirements \
     && mkdir /var/lib/kolla \
     && curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py \
     && python get-pip.py \
     && rm get-pip.py \
-    && pip install pip==7.1.2 \
     && pip --no-cache-dir install -U virtualenv \
     && virtualenv --system-site-packages /var/lib/kolla/venv \
-    && /var/lib/kolla/venv/bin/pip --no-cache-dir install pip==7.1.2 \
     && /var/lib/kolla/venv/bin/pip --no-cache-dir install --upgrade -c requirements/upper-constraints.txt \
         jinja2 \
         kazoo \