sandbox-ora: Allow to configure the user used by ORA
sandbox-ora: Add xqueue/ORA to sandbox & switch to `virtualenv` role
sandbox-ora: Add SERVICE_VARIANT to xqueue to customize filenames

To be used in conjonction with
https://github.com/antoviaque/xqueue/commit/303601ea9ffcbd30f6bb3e2b9a42d6f85fbcf6b3

This is necessary to be able to get several services using the
`/opt/wwc/env.json` & `/opt/wwc/auth.json` files. The configuration
files would get overwitten when this is used by several different
services cohabiting on a single instance
sandbox-ora: Fixes `NaN` in config when nb of cores is incorrectly detected
sandbox-ora: Add missing '/' in configuration of open ended interface
sandbox-ora: Switch to HTTP for contacting Xqueue to match LMS defaults
sandbox-ora: Allow to configure Rabbitmq binding IP & use localhost for sandbox
sandbox-ora: Create edx user expected by xqueue in rabbitmq
sandbox-ora: Parametrize the variables used for ORA's virtualenv
sandbox-ora: Create dedicated user & virtualenv for xqueue

Since xqueue has its own set of dependencies, using a dedicated
virtualenv allows to avoid potential dependencies conflicts when
several services are installed on the same instance.
sandbox-ora: Add SERVICE_VARIANT to ORA to customize filenames

This is necessary to be able to get several services using the
`/opt/wwc/env.json` & `/opt/wwc/auth.json` files. The configuration
files would get overwitten when this is used by several different
services cohabiting on a single instance
sandbox-ora: Allow to deactivate creation of the xqueue DB

The mysql_db command from ansible expects to be able to connect to the
`mysql` DB, which prevents changing the MySQL DB for xqueue to a
DB on which we don't have overall administrator privileges.

https://github.com/ansible/ansible/blob/devel/library/database/mysql_db
Merge pull request #234 from antoviaque/sandbox-ora

sandbox-ora: Include xqueue & ORA on the `edx_sandbox` playbook