The ring crypto library used by the simulator only accepts PEM keys in
PKCS#8 format; this provides a conversion of the original bundled key.
```
$ openssl pkcs8 -topk8 -nocrypt -in ../root-ec-p256.pem -out ../root-ec-p256-pkcs8.pem
```
Signed-off-by: Fabio Utzig <utzig@apache.org>
Fabio Utzig