misc: Added Dockerfile for Python3

This will create a docker image with all gem5 dependencies in a Python3
virtual environment.

Issue-on: https://gem5.atlassian.net/browse/GEM5-392
Change-Id: Id23777fb698977e92437c546f1fdf0ea0faa8708
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26506
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

util/dockerfiles/python3/Dockerfile

@@ -0,0 +1,37 @@
+# Copyright (c) 2020 The Regents of the University of California
+# All Rights Reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met: redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer;
+# redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution;
+# neither the name of the copyright holders nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+FROM ubuntu:18.04
+
+RUN apt -y update
+RUN apt -y upgrade
+RUN apt -y install build-essential git m4 scons zlib1g zlib1g-dev \
+    libprotobuf-dev protobuf-compiler libprotoc-dev libgoogle-perftools-dev \
+    python-dev python python3-dev python3.6 python-six python3-venv
+
+ENV VIRTUAL_ENV "/venv"
+RUN python3 -m venv $VIRTUAL_ENV
+ENV PATH "$VIRTUAL_ENV/bin:$PATH"