Strip all ANSI escape sequences from child log files

Closes #1768 and sadly partly reverts #1758

target/supervisor/supervisord.conf

@@ -9,7 +9,7 @@ password = docker-mailserver-password
 user = root
 loglevel = warn
 nodaemon = true
-strip_ansi = false
+strip_ansi = true
 logfile = /var/log/supervisor/supervisord.log      ; default $CWD/supervisord.log
 pidfile = /var/run/supervisord.pid                 ; default supervisord.pid
 childlogdir = /var/log/supervisor                  ; default $TEMP ('AUTO' child log dir)