devlxd: Do not return devlxd info if turned off
devlxd: Do not return devlxd info if turned off

This changes devlxd in that it will return HTTP Forbidden if
`security.devlxd` is false. Previously, a bad agent could still have
retrieved devlxd information if the socket was present as the LXD never
checked whether or not it was turned on and always served the endpoints.

Signed-off-by: Thomas Hipp <5f82c492b3b00e427412d216ce820707a10c51ce@canonical.com>

lxc/lxd,lxc/lxd,lxc/lxd,lxc/lxd,lxc/lxd,lxc/lxd,lxc/lxd