HostKeys missing file object access

[flxkid]

HostKeys load and __init__ methods should allow a file_obj much like the PKey class does so that keys can be loaded in a similar manner. The add method allows something similar, but the key must already be parsed out to use. I want to store my host keys in a table without having to strip anything. Right now I remove the openssh formatting and then load the key like this:

sshconn._system_host_keys.add(row["host"], "ssh-rsa", RSAKey(data=base64.decodestring(row["pub_key"])))