Add debug symbols to haproxy

Currently profiling CPU usage of haproxy is hampered by lacking debug symbols to decode the function names in the profiler output.

Currently we use a build of haproxy 1.8 from the following PPA: http://ppa.launchpad.net/vbernat/haproxy-1.8/ubuntu

A debuginfo package (haproxy-dbgsym) is available from that PPA: http://ppa.launchpad.net/vbernat/haproxy-1.8/ubuntu/dists/xenial/main/debug/binary-amd64/