Change version using python from 2 to 3

Related-bug: PRODX-2232
Change-Id: I297ef5a348ff0d3a9ecb49a1fd3cf626b61b93f3
diff --git a/Dockerfile b/Dockerfile
index b7759b4..c011b22 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -5,7 +5,6 @@
 COPY horizon/ opt/horizon
 RUN apt-get update && apt-get install -y \
     python3 \
-    python-dev \
     python3-dev \
     build-essential \
     libssl-dev \
@@ -13,7 +12,7 @@
     libxml2-dev \
     libxslt1-dev \
     zlib1g-dev \
-    python-pip \
+    python3-pip \
     firefox \
     xvfb \
     tox \
@@ -30,6 +29,5 @@
 
 WORKDIR /opt/horizon
 
-RUN pip install -r requirements.txt && \
-    pip install -r test-requirements.txt
+RUN pip3 install -r requirements.txt -r test-requirements.txt