Implement SSL/certificates support about lxd

[hallyn]

I've been working on this in github.com/hallyn/lxd #cert.4. The current state of it is:

Client and server talk over tlsv1.2.
Client and server create certificates at first startup.
Client sends his certificate to server at remote add time.
Server stores client certificates under /var/lib/lxd/clientcerts/[ServerName].
Server rejects communications (except trust/add, which will require password) from unknown certificates.
Server accepts password setting over /trust post.

The client does not yet present server certificate fingerprint for user to ok/deny.
The client does not check server certificates at connect time.
The server does not yet check the password at /trust/add.
(I'm probably forgetting other remaining gotchas)

The result at the moment is fully usable and an improvement over the current master branch, since at least communications are now encrypted.

This is all done over old-web interface. It'll all need to be switched to the specified rest apis. I figure we'll do all of that conversion at once, hopefully next week.

[hallyn]

The caveat about server not checking password at /trust/add is no longer applicable