Ensure literal keys get a non-blank comment

When adding a literal key, use "Added by clj-ssh" as the comment.

Author: hugoduncan

src/clj_ssh/ssh.clj

@@ -169,6 +169,7 @@
                 agent (as-bytes private-key) (as-bytes public-key))]
            (when passphrase
              (.decrypt keypair passphrase))
+           (.setPublicKeyComment keypair "Added by clj-ssh")
            (.add id-repo (.forSSHAgent keypair)))))
 
      (and public-key-path private-key-path)