message: Add Python 3 and pip3 to build_container_ubuntu.sh
  As suggested at
diff: @@ -5,8 +5,8 @@ set -e
  # Setup basic requirements and install them.
  apt-get update
  export DEBIAN_FRONTEND=noninteractive
  -apt-get install -y wget software-properties-common make cmake git python python-pip unzip \
  - bc libtool ninja-build automake zip time golang g++ gdb strace wireshark tshark tcpdump
  +apt-get install -y wget software-properties-common make cmake git python python-pip python3 python3-pip \
  + unzip bc libtool ninja-build automake zip time golang g++ gdb strace wireshark tshark tcpdump
  # clang 7.
  wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
  apt-add-repository "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-7 main"
  @@ -27,7 +27,7 @@ chmod 750 /usr/sbin/tcpdump
  setcap cap_net_raw,cap_net_admin=eip /usr/sbin/tcpdump
  # virtualenv
  -pip install virtualenv
  +pip3 install virtualenv
  EXPECTED_CXX_VERSION="g++ (Ubuntu 5.4.0-6ubuntu1~16.04.11) 5.4.0 20160609" ./build_container_common.sh
  