Generate private keys in PEM format

Currently paramiko do not support Keys in RFC4716 format that
have landed with the buster update.
So any keys need to be generated in legacy PEM format.

Fixes: APERTIS-5932
Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>

test-cases/sdk-ade-remote-debugging.yaml

@@ -40,7 +40,7 @@ run:
     - "Install an ARM 32bit sysroot on the host"
     - $ ade sysroot install
     - "Enable key-based SSH login on the target device"
-    - $ ssh-keygen
+    - $ ssh-keygen -t rsa -m PEM
     - $ ssh-copy-id USER@HOST
     - "Clone the source code for the HelloWorld sample agent on the SDK host"
     - $ git clone https://gitlab.apertis.org/sample-applications/helloworld-simple-agent