Merge branch 'metis-tests' into 'master'

 METIS fixes

Code to re-scale the METIS weights in an attempt to avoid large ranges
that fail to produce a complete partition. If that still happens then
handle that case by continuing with the current partition, noting this
problem with a warning.

Also adds function to dump the METIS graphs, possibly separated
into only weights for off-line analysis.

See merge request !61