[trace-agent] restart on unexpected error code

This patch restarts the trace agent if it exits with an error code
that is different from 0. Else, it would restart in some cases but
would consider as 'expected' the return code 2 which is what Go
returns for builtin runtime errors.

Author: ufoot

packaging/supervisor.conf

@@ -75,6 +75,8 @@ startsecs=5
 startretries=3
 priority=998
 user=dd-agent
+autorestart=unexpected
+exitcodes=0
 
 [group:datadog-agent]
 programs=forwarder,collector,dogstatsd,jmxfetch,go-metro,trace-agent