util: Add error handling to become_daemon()

util: Add error handling to become_daemon()

Log failure and exit if fork() or setsid() fails.

Leave the logic in the non-setsid() code as it is.  This is probably
meant to fall through on failure of either opening /dev/tty or
ioctl().  Documentation for the ioctl() failure case is far from
clear.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Thu Aug 17 11:48:32 CEST 2017 on sn-devel-144