紧急制动
超级管理员在极端情况下的维护手段，开启紧急制动模式后，链上只接收超级管理员发送的治理交易，其他交易全部拒绝。（治理交易为本章的管理员操作）
主要使用场景为进行一些升级，维护等操作时，不希望有其他交易干扰。
开启
$ cldi emergency-brake on
tx_hash: 0x5b5aaa42b4312fb204a156d279e0f98805e62a98cdf9293c4d5f361fcefc3d88
等待几秒，待交易上链之后，将只有超级管理员可以发送治理交易，普通用户和普通交易会返回forbidden错误。
例如使用普通用户账户test创建合约：
$ cldi account login test
OK, now the default user is `test`, account addr is 0x415f568207900b6940477396fcd2c201efe49beb
$ cldi create 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
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Status { code: InvalidArgument, message: "Expect error: forbidden", metadata: MetadataMap { headers: {"content-type": "application/grpc", "date": "Wed, 21 Jul 2021 09:05:37 GMT"} }, source: None }', src/client.rs:146:14
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
关闭
$ cldi emergency-brake off
tx_hash: 0x347cf8a7ef89958e936344dc8318fd0ca7dd5eadaab60df74f094989549b7427
等待几秒，待交易上链之后，普通用户就可以再次正常发送交易了。
$ cldi account login test
OK, now the default user is `test`, account addr is 0x415f568207900b6940477396fcd2c201efe49beb
$ cldi create 0x608060405234801561001057600080fd5b5060f58061001f6000396000f3006080604052600436106053576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff16806306661abd1460585780634f2be91f146080578063d826f88f146094575b600080fd5b348015606357600080fd5b50606a60a8565b6040518082815260200191505060405180910390f35b348015608b57600080fd5b50609260ae565b005b348015609f57600080fd5b5060a660c0565b005b60005481565b60016000808282540192505081905550565b600080819055505600a165627a7a72305820faa1d1f51d7b5ca2b200e0f6cdef4f2d7e44ee686209e300beb1146f40d32dee0029
tx_hash: 0x7eeaefdf3d266a2b1a8b6350952b1353b230207bc4c089735a3d2e482dc1f77e