Make lxc.functions return the default lxcpath if /etc/lxc/lxc.conf doesn't provide one

Currently it returns the default path only if /etc/lxc/lxc.conf missing.
Since default lxc.conf doesn't contain lxcpath variable (this is at least the case in ubuntu) all tools fails if one doesn't give -P

caglar@qgq:~/Project/lxc/examples$ sudo /usr/bin/lxc-create -n test
lxc-create: no configuration path defined

Signed-off-by: S.Çağlar Onur <caglar@10ur.org>