This plugin has been used at Redpill Linpro for some time now. It adds
some measurements compared to varnish4_ and removes some others.
There are enough changes that it is probably not worth it to try to
merge the code into a generic varnish4_ plugin handling 4, 5 and 6.
If you make a symlink like varnish4_shop_request_rate (etc.), you can
add plugin configuration
[varnish4_shop_*]
env.name shop
and it will run all commands with -n shop to get the stats for that instance.
Varnish4_ plugin displays categories in an arbitrary order, changing
the colors of the graphs with each run.
This fix introduces a 'sort' statement in the category iteration function
to force the same order consistently.
