As a followup to Id99948aec64656a0532afc68e146f0610bff1378, adding auto
detection to haproxy_amphora.user_group
haproxy is capable[1] handling a list of configuration files.
This patch leverages that capability by simply providing haproxy with an
additional configuration file, which is baked in the amphora image via a
diskimage-builder element.
The above-mentioned element will specify the following values for user group:
Ubuntu: 'nogroup'
RHEL/CentOS/Fedora: 'haproxy'
The amphora-agent will parse and remove any user_group configuration provided
by Octavia controller worker.
This is in order to maintain amphora-agent backward compatibility to old
Octavia workers, who still provide user_group to the amphora-agent.
Octavia Workers that include this patch will no longer provide user_group
configuration to the amphora-agent.
[1] https://cbonte.github.io/haproxy-dconv/1.7/management.html#3
Related-Bug #1548070
Change-Id: Ia8fede9d7da4709a48661d1fc595a16d04fcbfa9
26a55415ab