new config option, stdout/stdin closed

Now stdin and stdout get closed. Additionally stderr gets closed and
reopened to the new config option „logfile“ if specified

repmgr.conf.sample

@@ -42,3 +42,8 @@ pg_bindir=/usr/bin/
 # you may add command line arguments for pg_ctl
 #
 # pg_ctl_options='-s'
+
+#
+# redirect stderr to a logfile
+#
+# logfile='/var/log/repmgr.log'