Pass timeout_options to bulk_index

This allows clients of bulk_index to specify the timeout options, rather
than accepting a client object instance, which clients of Index cannot
easily construct.
Use a longer timeout when bulk indexing

There are intermittent timeouts when bulk indexing. The bulk-reindex
needs to be reliable and may place a temporary higher load on the
elastic search server leading to operations taking a bit longer.
Merge pull request #168 from alphagov/longer-bulk-load-timeout

Longer bulk load timeout