Adding aws vars for common role to work

The AWS vars need to be added because the common/templates/etc/logrotate.d/hourly/edx_logrotate_tracking.j2 calls the variable {{ aws_s3_sync_script }}
If we do hardcode the path I think we should probably use `{{ COMMON_BIN_DIR }}/send-logs-to-s3` and ensure that a symlink is created from there to the location in the aws role, how does that sound?