lxd: read the stored client certs at startup

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
add newly acquird client certs to daemon.clientCA

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
add first instance of checking for stored client cert

list.go just reports on console whether cert was stored or not,
for testing purposes.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>