benchmark-report: Allow non-ASCII characters for plot labels.
benchmark-report: Add matplotlib configuration file example to override the font being used.

This is required for report including Japanese characters as Bitstream
font (the default) does not handle such characters.
benchmark-report: Fix sorting by number of users.

Eg, instead of 1, 6 and 12, it was being sorted as 1, 12 and 6 users.