* generate fresh keys for user if no keys provided

this would ideally be stored in the ssh agent and not in the file
system
as a first pass its ok to go with file system

* generate fresh key pair, sign cert and write to file system

if no key specified then generate keys and get that signed

* fix: sort extensions in lexical order

* feat: if no key provided then generate keys, cert and write to agent

* fix: let client handle filenames

* chore: do not pass key file name to ca server, remove unused methods

* fix: host test config