[autotest] Update login_OwnershipApi to use protobufs

client/cros/ownership.py

Index: client/cros/ownership.py
diff --git a/client/cros/ownership.py b/client/cros/ownership.py
index 0acd767d5cab43287dcd2a7ab5d927c839cb49a0..462c247f4e7b3505b3a20d35b5070b2fe1f3f0f4 100644
--- a/client/cros/ownership.py
+++ b/client/cros/ownership.py
@@ -65,8 +65,8 @@ def pairgen():
 
     The caller is responsible for cleaning up these files.
     """
-    keyfile = scoped_tempfile.tempdir.name + 'private.key'
-    certfile = scoped_tempfile.tempdir.name + 'cert.pem'
+    keyfile = scoped_tempfile.tempdir.name + '/private.key'
+    certfile = scoped_tempfile.tempdir.name + '/cert.pem'
     cmd = '%s -x509 -subj %s -newkey rsa:2048 -nodes -keyout %s -out %s' % (
         OPENSSLREQ, '/CN=me', keyfile, certfile)
     system_output_on_fail(cmd)
@@ -164,4 +164,3 @@ def sign(pem_key_file, data):
     if not sig_data:
         raise error.TestFail('Empty signature!')
     return sig_data
-