[mgmt slave] Install correct version of python-cffi (#760)

sonic-mgmt/Dockerfile

@@ -26,6 +26,9 @@ RUN apt-get install -y default-jre
 # For syslog test
 RUN apt-get install -y rsyslog psmisc
 
+# Remove cffi 1.5.2, will install 1.10.0 by pip later
+RUN apt-get remove -y python-cffi python-cffi-backend
+
 RUN easy_install pip
 
 RUN pip install ipaddr \
@@ -37,6 +40,7 @@ RUN pip install ipaddr \
                 pyasn1==0.1.9 \
                 pysnmp==4.2.5 \
                 jinja2==2.7.2 \
+                cffi==1.10.0 \
                 paramiko==2.1.2
 
 RUN git clone https://github.com/ansible/ansible