When loading SSH keys from X509 certificates ignore things outside of the armor

[adiroiban]

RIght now, when loading SSH key from X509 cert, the PEM should contain a single object and the armor should be the first thing in the file.

We should relax this to allow for "PEM comments" for example

BagAttribute=bla
---- BEGIN CERTIFICATE ---
TRALA

[adiroiban]

This is not fixed in chevah-keycert .... it is fixed in chevah/server where the config allows multiple PEMs.

I guess that for keycert we should to something similar:

1. Try loading using Python pem library and detect the type based on what pem tells us.
2. If nothing is returned by pem ... try to read anything outside of pem armors... this might need an update in pem library... or add custom code in chevah-keycert similar to the code in chevah/server