gpg: handle KILLAGENT command

so `gpg-connect-agent KILLAGENT` should stop the running agent

trezor_agent/gpg/__main__.py

@@ -112,6 +112,9 @@ def main_agent():
             with contextlib.closing(conn):
                 try:
                     agent.handle_connection(conn)
+                except StopIteration:
+                    log.info('stopping gpg-agent')
+                    return
                 except Exception as e:  # pylint: disable=broad-except
                     log.exception('gpg-agent failed: %s', e)
 

trezor_agent/gpg/agent.py

@@ -142,6 +142,9 @@ def handle_connection(conn):
             keyring.sendline(conn, fmt.format(keygrip).encode('ascii'))
         elif command == b'BYE':
             return
+        elif command == b'KILLAGENT':
+            keyring.sendline(conn, b'OK')
+            raise StopIteration
         else:
             log.error('unknown request: %r', line)
             return