Fix check for openpty

The previous implementation of the openpty check was always returning
'no' as openpty is typically defined in util.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
lxcutmp.c: Fix typo causing build failure

In a previous change I added an ifdef for HAVE_SYS_TIMERFD_h
rather than HAVE_SYS_TIMERFD_H, leading to a missing include of
sys/timerfd.h on platforms that support it and ultimately to a build
failure.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>