Don't use SSH agent when connecting to test VMs

It's not helpful, and if the agent setup is broken or the agent is unhealthy
then contacting the agent can break us.

Author: rocallahan

release-process/test-system.py

@@ -115,6 +115,8 @@ def ssh_command(self):
     def ssh_options(self):
         return ['-i', self.keypair_pem_file,
                 '-o', 'StrictHostKeyChecking=no',
+                # A broken agent config can stop SSH from working. Bypass that.
+                '-o', 'IdentityAgent=none',
                 '-o', 'BatchMode=yes',
                 '-o', 'ConnectTimeout=5',
                 '-o', 'IdentitiesOnly=yes']