Do not sort site coordinates if site_ids are provided by user
Do not sort site coordinates if site_ids are provided by user

Calculations starting from ground motion fields input by the user require at least two input files related to the gmf data:
1. A sites.csv file, listing {site_id, lon, lat} tuples
2. A gmfs.csv file, listing {event_id, site_id, gmv[IMT1], gmv[IMT2], ...} tuples

The site coordinates defined in the sites file do not need to be in sorted order; the only requirement should be to ensure there is not duplication of either the site_ids or the coordinates.

However currently, when creating the site mesh from the site coordinates read from the csv file, the coordinates get sorted and are assigned new site ids, breaking the link with the user-specified site_ids and thus also with the gmf data.

This patch will avoid sorting the coordinates when the site_ids are provided in the user input sites file.

Former-commit-id: d1971fc7daedc27f38fa4f0319c0189dc890c6ae [formerly 436eb5117cc39891de67cf97b552ccad142e1019]
Former-commit-id: 0ddd17394bacf83292b0b7a4562622272a786500
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine