Add a new logger: syslog and Print the VM name in the logs

Add a new logger: syslog and Print the VM name in the logs

To activate it specify lxc.syslog = <afacility>
For now the available facilities are: daemon, local[0-7] others will be
rejected

syslog got only activated after the function that checks for inheritance
of fd is passed in order to make sure the syslog fd is not inherited
and prevent the creation of the fd is any log have been issued during
the checks (which would end up in an infinite loop)

Signed-off-by: Fatih ACAR <fatih.acar@gandi.net>
Signed-off-by: Ahmed Amamou <ahmed@gandi.net>
Signed-off-by: Baptiste Daroussin <bapt@gandi.net>
Signed-off-by: William Dauchy <william@gandi.net>