CA-47802: improve logging from fork/exec daemon
CA-47802: improve logging from fork/exec daemon

1. we now log even successful process exits
   -- useful for debugging other services
2. in the case when xapi calls "dontwaitpid" (currently implemented by closing
   the connection to the control socket) don't misinterpret the EPIPE as an
   error and spam syslog with lots of unnecessary internal debugging stuff

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

djs55/forkexecd,xapi-project/message-switch,xapi-project/message-switch,johnelse/forkexecd,xapi-project/message-switch