Fixes for edxapp: Permissions & supervisor startup/configuration

This fixes the edxapp role and allows it to complete. Applied on a new VM with `edx_sandbox.yml`, on the current master edxapp is currently failing over several errors: permissions (staticfiles folder, virtualenv files only readable by edxapp), order of execution (link to python executable before it is created) and supervisor commands (loading new config files & startup) -- cf individual commits.