[PROD-15230] Add python-virtualenv in Jenkins master

In the case of slaveless deployment, jobs are executed on master and
therefore it is necessary to have python-virtualenv installed on master.

Change-Id: I917853d4dc3039007d849722265d757a3014a4a1
(cherry picked from commit 38477c31329dd15386fe4686e0e584c3daad6f35)
diff --git a/Dockerfile b/Dockerfile
index 3cf4aac..68a5104 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,6 @@
 FROM openjdk:8-jdk
 
-RUN apt-get update && apt-get install -y git curl gettext-base && rm -rf /var/lib/apt/lists/*
+RUN apt-get update && apt-get install -y git curl gettext-base python-virtualenv && rm -rf /var/lib/apt/lists/*
 
 ENV JENKINS_HOME /var/jenkins_home
 ENV JENKINS_SLAVE_AGENT_PORT 50000