Configurable ES timeouts

[noirbizarre]

This PR makes the Elasticsearch timeouts configurable through:

• ELASTICSEARCH_TIMEOUT as default/read/query timeout
• ELASTICSEARCH_INDEX_TIMEOUT as indexing/write timeout (longuer timeout)
• the -t/--timeout in udata search index command (overrides ELASTICSEARCH_INDEX_TIMEOUT if provided)

This allows to improve control over timeout and so will allows to handle indexing errors such as:

elasticsearch.exceptions.ConnectionTimeout: ConnectionTimeout caused by - ReadTimeoutError(HTTPConnectionPool(host=u'localhost', port=9200): Read timed out. (read timeout=10))

Possible improvement: do the same for retry policy