Force PEM SSH keys for paramiko

Trying to get ansible-test working on my fedora-28 system, I noticed I
was getting invalid keys from paramiko. It looks like this is because
ssh-keygen is now defaulting to RFC4716 format for private / public
keys.

For now, we can still use PEM based SSH keys, but the long term fix here
is to report a bug to paramiko and support RFC4716 for rsa keys.

Signed-off-by: Paul Belanger <pabelanger@redhat.com>

test/runner/lib/core_ci.py

@@ -542,7 +542,7 @@ class SshKey(object):
                 make_dirs(base_dir)
 
             if not os.path.isfile(key) or not os.path.isfile(pub):
-                run_command(args, ['ssh-keygen', '-q', '-t', 'rsa', '-N', '', '-f', key])
+                run_command(args, ['ssh-keygen', '-m', 'PEM', '-q', '-t', 'rsa', '-N', '', '-f', key])
 
             if not args.explain:
                 shutil.copy2(key, self.key)