Add pymongo in panko images

Panko need pymongo library when mongo is used as panko
backend.

Change-Id: I1763ef2af2f5d13a5195eb105c2901e1ba44a854
Closes-Bug: #1681776

docker/panko/panko-api/Dockerfile.j2

@@ -7,7 +7,11 @@ MAINTAINER {{ maintainer }}
 
 {% if install_type == 'binary' %}
     {% if base_distro in ['centos', 'oraclelinux', 'rhel'] %}
-       {% set panko_api_packages = ['openstack-panko-api'] %}
+       {% set panko_api_packages = [
+            'openstack-panko-api',
+            'python-pymongo'
+        ] %}
+
     {% elif base_distro in ['debian', 'ubuntu'] %}
 
 RUN echo '{{ install_type }} not yet available for {{ base_distro }}' \

docker/panko/panko-base/Dockerfile.j2

@@ -55,7 +55,8 @@ RUN truncate -s 0 /etc/apache2/ports.conf
 ADD panko-base-archive /panko-base-source
 
 {% set panko_base_pip_packages = [
-    '/panko'
+    '/panko',
+    'pymongo'
 ] %}
 
 RUN ln -s panko-base-source/* panko \