feat: [BC] Python 2 for all target platforms (#160)

* feat: python-is-python3 and move build essentials to base

* feat: use manual symlink instead and include pip3

* fix: derp

* fix: python already exists

* feat: add python install

* Apply suggestions from code review

Co-authored-by: David Finol <davidmfinol@gmail.com>

* go back to installing python2

Co-authored-by: David Finol <davidmfinol@gmail.com>

* remove symlinks

Co-authored-by: David Finol <davidmfinol@gmail.com>

* redistribute installations based on their weight

Co-authored-by: David Finol <davidmfinol@gmail.com>

images/ubuntu/base/Dockerfile

@@ -27,6 +27,8 @@ RUN apt-get -q update \
  libxss1 \
  cpio \
  lsb-release \
+ python \
+ python-setuptools \
  xvfb \
  xz-utils \
  && apt-get clean \
@@ -50,7 +52,7 @@ RUN apt-get -q update \
  && apt-get -q install -y --no-install-recommends software-properties-common \
  && add-apt-repository -y ppa:ubuntu-toolchain-r/test \
  && apt-get -q install -y --only-upgrade libstdc++6 \
- && add-apt-repository -y --remove ppa:ubuntu-toolchain-r/test \ 
+ && add-apt-repository -y --remove ppa:ubuntu-toolchain-r/test \
  && apt-get -q remove -y --auto-remove software-properties-common \
  && apt-get clean \
  && rm -rf /var/lib/apt/lists/*

images/ubuntu/editor/Dockerfile

@@ -173,7 +173,7 @@ RUN echo "$version-$module" | grep -q -vP '^20(?!18).*android' \
   && apt-get clean \
   && rm -rf /var/lib/apt/lists/* \
   # Accept licenses
-  && yes | "${ANDROID_HOME}/tools/bin/sdkmanager" --licenses \  
+  && yes | "${ANDROID_HOME}/tools/bin/sdkmanager" --licenses \
   \
   # Update alias 'unity-editor'
   && { \
@@ -206,21 +206,11 @@ RUN echo "$module" | grep -q -v '\(webgl\|linux-il2cpp\)' \
   || : \
   && apt-get -q update \
   && apt-get -q install -y --no-install-recommends --allow-downgrades \
-    python \
-    python-setuptools \
     build-essential \
     clang \
   && apt-get clean \
   && rm -rf /var/lib/apt/lists/*
 
-#=======================================================================================
-# [android, ios] python 3 support
-#=======================================================================================
-RUN echo "$module" | grep -q -v '\(android\|ios\)' \
-  && exit 0 \
-  || : \
-  && ln -s /usr/bin/python3 /usr/bin/python
-
 #=======================================================================================
 # [2019.x] libnotify4 libunwind-dev libssl1.0
 #=======================================================================================