MEDIUM: haproxy-systemd-wrapper: Use haproxy in same directory

Locate the wrapper and use a haproxy executable found in the
same directory.

This patch lets the wrapper work in openSUSE.
MEDIUM: systemd-wrapper: Kill child processes when interrupted

Send SIGINT to child processes when killed. This ensures that
the haproxy process managed by the systemd-wrapper is stopped
when "systemctl stop haproxy.service" is called.
LOW: systemd-wrapper: Write debug information to stdout

Write the command line used to call haproxy to stdout, as
well as the return code returned by the haproxy process.