mod_proxy: Improve the balancer member data shown

in mod_status when "ProxyStatus" is "On":
add "busy" count to auto mode and show byte counts
in auto mode always in units of kilobytes.

Partial backport of r1837588 from trunk
(only auto mode changes, html parts not yet
backported).

Submitted by: rjung
Reviewed by: rjung, jim, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1839532 13f79535-47bb-0310-9956-ffa450edef68