Install MySQL-python with pip in openstack-base container (type source)

MySQL-python is required by the Horizon database session cache.

Change-Id: I620767bc10f3316ed1037d86f5f6729066bfcfbd
Closes-bug: #1630559

docker/openstack-base/Dockerfile.j2

@@ -200,7 +200,6 @@ ENV DEBIAN_FRONTEND noninteractive
             'libxslt-devel',
             'libyaml-devel',
             'MariaDB-devel',
-            'MySQL-python',
             'openldap-devel',
             'openssl-devel',
             'postgresql',
@@ -274,6 +273,7 @@ RUN curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py \
         'kombu',
         'monotonic',
         'msgpack-python',
+        'MySQL-python',
         'netaddr',
         'netifaces',
         'os-client-config',