tests: Implement test_fcntl_lock correctly

tests: Implement test_fcntl_lock correctly

This does:

openat(AT_FDCWD, "/tmp/test_socket_wrapper_Win6aA/file", O_RDWR|O_CREAT, 0600) = 3
fcntl(3, F_OFD_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=1}) = 0
write(3, "fd=3\n", 5)                   = 5
fcntl(3, F_OFD_SETLK, {l_type=F_UNLCK, l_whence=SEEK_SET, l_start=0, l_len=1}) = 0
unlink("/tmp/test_socket_wrapper_Win6aA/file") = 0                                                                                                                                   close(3)
close(3)                                = 0

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>