confine/*.lua: fix mgmt_net.addr
confine/*.lua: fixing node error handling and tinc invalid mgmt_net handling
confine/*.lua: ensure (even empty) node and sliver errors array
confine.lib: fix slivers management and private IPv6 addresses
confine/*.lua: provide appropriate error messages for invalid
id, cert, arch, local_ifname, sliver_pub_ipv6, sliver_pub_ipv4, and sliver_pub_ipv4_range values.
Related to http://redmine.confine-project.eu/projects/confine/issues 60-64