fixing dockerfile to include a dependency on python

Change-Id: I39311eef087102b01b498baff9a257999f471d9c
diff --git a/tools/build/docker/Dockerfile b/tools/build/docker/Dockerfile
index ee9666a..3c688fa 100644
--- a/tools/build/docker/Dockerfile
+++ b/tools/build/docker/Dockerfile
@@ -20,7 +20,7 @@
 
 #Download and Build ONOS
 WORKDIR /src
-RUN     apt-get update && apt-get install -y maven git curl oracle-java8-installer oracle-java8-set-default && \
+RUN     apt-get update && apt-get install -y python maven git curl oracle-java8-installer oracle-java8-set-default && \
         git clone https://github.com/opennetworkinglab/onos.git && cd onos && \
         mkdir -p /root/Downloads && \
         mvn clean install && \