Install ipython from packages (#637)

dockers/docker-ptf/Dockerfile.j2

@@ -42,6 +42,7 @@ RUN sed --in-place 's/httpredir.debian.org/debian-archive.trafficmanager.net/' /
         libqt5core5a        \
         libqt5network5      \
         less                \
+        ipython             \
         iputils-ping
 
 
@@ -71,7 +72,6 @@ RUN rm -rf /debs \
     && pip install dpkt    \
     && pip install ipaddress \
     && pip install pysubnettree \
-    && pip install 'ipython<6.0' \
     && pip install paramiko \
     && pip install parallel-ssh \
     && mkdir -p /opt       \