Make metric names configurable
Make metric names configurable

Users now have the ability to overwrite the metric names for frontends/
backends/servers by setting a list of names separated by space in the
'process' section, example::

    [process]
    src-dir       = ${paths:base-dir}/incoming
    workers       = 1
    server-metrics = bin bout
    frontend-metrics = ereq dreq
    backend-metrics = lbtot qmax

We should do the same for average metrics and also perform a sanity
check on the input from user.

unixsurfer/haproxystats,unixsurfer/haproxystats,unixsurfer/haproxystats