fix compilation warnings

fix compilation warnings

Fix the following warnings:

console.c: In function ‘console_handler’:
console.c:252: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result
console.c:254: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result
conf.c: In function ‘instanciate_veth’:
conf.c:1130: warning: ignoring return value of ‘mktemp’, declared with attribute warn_unused_result
conf.c:1135: warning: ignoring return value of ‘mktemp’, declared with attribute warn_unused_result
conf.c: In function ‘instanciate_macvlan’:
conf.c:1206: warning: ignoring return value of ‘mktemp’, declared with attribute warn_unused_result
af_unix.c: In function ‘lxc_af_unix_send_fd’:
af_unix.c:124: warning: dereferencing type-punned pointer will break strict-aliasing rules
af_unix.c: In function ‘lxc_af_unix_recv_fd’:
af_unix.c:169: warning: dereferencing type-punned pointer will break strict-aliasing rules
af_unix.c: In function ‘lxc_af_unix_send_credential’:
af_unix.c:195: warning: dereferencing type-punned pointer will break strict-aliasing rules
af_unix.c: In function ‘lxc_af_unix_rcv_credential’:
af_unix.c:237: warning: dereferencing type-punned pointer will break strict-aliasing rules

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>