sshkey template should validate the data inside the self.validate() method

[zaibon]

See the documentation about validate() method: https://github.com/Jumpscale/0-robot/tree/master/docs/services#validate-service-data-received-during-creation

[chrisvdg]

All the logic is in the constructor, but validation is run after that has been called and the key should be loaded already so dir and passphrase aren't actually really needed anymore. @zaibon, so either the logic needs to move to install or validate should check if the key has been loaded or something?