Adds python role, which installs python 2.7 using raw ansible commands.

The python role is prepended to edx_sandbox.yml and edx-stateless.yml in a
prefix playbook, so that gather_facts can be "no".

playbooks/edx-stateless.yml

@@ -3,6 +3,13 @@
 # Stateless app server configuration, designed to be used with external mysql,
 # mongo, rabbitmq, and elasticsearch services.
 
+- name: Bootstrap instance(s)
+  hosts: all
+  gather_facts: no
+  become: True
+  roles:
+    - python
+
 - name: Configure instance(s)
   hosts: all
   become: True

playbooks/edx_sandbox.yml

@@ -4,6 +4,13 @@
 # for single server community
 # installs
 
+- name: Bootstrap instance(s)
+  hosts: all
+  gather_facts: no
+  become: True
+  roles:
+    - python
+
 - name: Configure instance(s)
   hosts: all
   become: True

playbooks/roles/python/defaults/main.yml

+# Install python2.7 + the /usr/bin/python symlink.
+
+python_packages:
+  - python-minimal

playbooks/roles/python/tasks/main.yml

+# Bootstrap packages must be installed with raw commands, because ubuntu
+# xenial+ cloud images don't have python2.7 installed, and ansible doesn't yet
+# support python3.
+
+- name: Update apt-get
+  raw: apt-get update -qq
+
+- name: Install packages
+  raw: "apt-get install -qq {{ item }}"
+  with_items: "{{ python_packages }}"