CLI should indicate failure when "15. Set transcoder config" is invoked on a block within the RoundLockAmount

Nobody has claimed this yet.

**Describe the bug**
If process `15. Set transcoder config` is invoked from the CLI when the current block is within `RoundLockAmount` of the next round, the CLI prints the following message:

```
Transaction sent. Once confirmed, please restart your node if the ServiceURI has been reset
```

This is incorrect since the transaction isn't created. The CLI should print a clear message that the parameters cannot be changed due to the `RoundLockAmount` restriction.

**To Reproduce**
Steps to reproduce the behavior:
1. Launch the CLI.
2. Invoke `15. Set transcoder config`.
3. Provide parameter values (they can be the same or different as the previous values).
4. Check transactions coming from your transcoder's address (e.g. via Etherscan) and you will see that no transaction is created.

**Expected behavior**
When the current block is within `RoundLockAmount` of the next round, I expect the CLI to provide an error stating that a transaction for parameter change cannot be created.

Start with the CLI entry point for `15. Set transcoder config` and reproduce the case where the current block is within `RoundLockAmount` of the next round. Trace transaction creation and failure reporting; done when this condition produces a clear error and no success message, with coverage for the restricted case.

Written by the indexing model from the issue text.