Use instrument database for generating focalplane model about desimodel

[sbailey]

FYI see the DESI wiki under Pipeline/RawDataTransfer#OperationsDatabase for information about how to access the read-only mirror of the ICS database at NERSC (and only visible from within NERSC, but I don't want to post the full info in a public ticket). Users can add those credentials to their .pgpass file at NERSC but we should not include that in the desimodel code itself (even if it is read-only and hidden behind NERSC credentials blah blah).

[sbailey]

Adding a note to prevent possible duplicated effort: @julienguy will take a first pass at this, updating the desi_generate_focalplane script to take a new parameter to load params from the database as an alternative to --pos_settings to get it from an SVN checkout of the files that were used to originally load the DB.

Possible gotcha: desi_generate_focalplane requires the configobj library, which isn't one of our standard dependencies and wasn't pre-installed on my laptop. "conda install configobj" easily fixed that, but it is highly likely that it isn't pre-installed in our latest desiconda release at NERSC either (but cori is still down so I can't immediately verify). If this is an issue ping me and we can discuss options.