Do not leak fds in case of failures setting up a child process
Resolves:
https://fedorahosted.org/sssd/ticket/3006
The handling of open pipes in failure cases was suboptimal. Moreover,
the faulty logic was copied all over the place. This patch introduces
helper macros to:
- initialize the pipe endpoints to -1
- close an open pipe fd and set it to -1 afterwards
- close both ends unless already closed
These macros are used in the child handling code.
The patch also uses child_io_destructor in the p11_child code for safer
fd handling.
Reviewed-by: Petr Cech <pcech@redhat.com>