Fail more quickly on too large ncss requests

[haileyajohnson]

To avoid long, unsuccessful ncss requests, look into calculating the data download size as soon as possible.

[edesfandiari]

A netcdf subset service (ncss) request for a large file download can almost take an
hour to return a "Request Too Large"! Following is an example and maybe a possible
solution to shorten that time.

The approximate final file size may be determined from the ncss cache file that
is produced almost immediately. For example, a ncss query immediately produced
ncss-grid218435382.nc (50980 bytes). Fifty five minutes later, it grow to over 9GB
before returning a "Request Too Large: Too large, max size = 5192000000".

Examining the dimensions in the short 50980 bytes file (e.g. ncdump, below) may
be used to estimate the final file size.

ncdump -h /var/lib/tomcats/ops/content/thredds/cache/ncss/ncss-grid218435382.nc
netcdf ncss-grid218435382 {
dimensions:
      lon = 3600 ;
      time = 365 ;
      lat = 1800 ;

This yields a file size of 3600 x 365 x 1800 x 4bytes = ~9.5GB which can be compared
the allowed maximum size.

[haileyajohnson]

This should be fixed by Unidata/netcdf-java#1213