fix a typo in test_pxe_server.py
fix a typo in test_pxe_server.py

zstackio/zstack-woodpecker,zstackorg/zstack-woodpecker,zstackorg/zstack-woodpecker,zstackio/zstack-woodpecker,zstackorg/zstack-woodpecker,zstackio/zstack-woodpecker