Fixes kolla_toolbox failure due to missing pytz module

kolla_toolbox contantly fails to build due to a missing module pytz,
add it before the dependent module installation.

Change-Id: Ia497f4eef830259e8e27307d6b3100dc7660b99f
Closes-Bug: #1569633

docker/kolla-toolbox/Dockerfile.j2

@@ -35,6 +35,7 @@ RUN apt-get -y --no-install-recommends install \
 RUN curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py \
     && python get-pip.py \
     && rm get-pip.py \
+    && pip --no-cache-dir install pytz \
     && pip --no-cache-dir install \
         MySQL-python \
         os-client-config==1.16.0 \