Update abstractions/ssl_* for acmetool-generated certificates

acmetool is an alternative client for Let's Encrypt.
(https://github.com/hlandau/acme/)

It stores the certificates etc. in the following directory layout:

    /var/lib/acme/live/<domain> -> ../certs/<hash>
    /var/lib/acme/certs/<hash>/cert
    /var/lib/acme/certs/<hash>/chain
    /var/lib/acme/certs/<hash>/privkey -> ../../keys/<hash>/privkey
    /var/lib/acme/certs/<hash>/url
    /var/lib/acme/certs/<hash>/fullchain
    /var/lib/acme/keys/<hash>/privkey

This patch adds the needed permissions to the ssl_certs and ssl_keys
abstractions so that the certificates can be used.


Acked-by: Seth Arnold <seth.arnold@canonical.com> for trunk, 2.10 and 2.9.