trivial: lib: fail hard on failed mallocs

It's pretty safe to not even bother checking for NULL when
using malloc and friends, but if we do check, then fail
hard.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Message-Id: <1447102433-20322-1-git-send-email-drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>