Changes for Tower virtualenv support

* Break requirements down into ansible and tower reqs
* Generate separate Ansible and Tower virtual environments
* Install appropriate requirements files into each one
* Modify development tools to use these venvs instead of our old
  site-packages
* Modify settings to indicate venv enablement and location of venvs
* Modify tasks to use the proper virtual environment for its purpose

tools/docker-compose/start_development.sh

@@ -21,7 +21,7 @@ else
 fi
 
 rm -rf /tower_devel/ansible_tower.egg-info
-mv /tmp/ansible_tower.egg-info /tower_devel/
+cp -R /tmp/ansible_tower.egg-info /tower_devel/
 
 # Check if we need to build dependencies
 if [ -f "awx/lib/.deps_built" ]; then
@@ -31,6 +31,9 @@ else
     touch awx/lib/.deps_built
 fi
 
+rm -rf /tower_devel/venv/tower/lib/python2.7/site-packages/ansible-tower.egg-link
+cp /tmp/ansible-tower.egg-link /tower_devel/venv/tower/lib/python2.7/site-packages/ansible-tower.egg-link
+
 # Tower bootstrapping
 make version_file
 make migrate