rotatingfile: mark log files as close-on-exec
The log file descriptor associated with the virRotatingFile
struct should be marked close-on-exec, as even when virtlogd
re-exec's itself it expect to open the log file fresh. It
does not need to preserve the logfile handles, only the network
client FDs.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>