Add a blockchain_enabled flag

[arturgontijo]

We should add a flag to these tools to make users able to test their services without using a blockchain.

If I call my service that has the Daemon's flag "blockchain_enabled": false, CLI spends about 11 seconds to get the response.
If I call it directly, using the gRPC module, it spends about 4 seconds.

Another important issue is that I've figured out that if I spawn a bunch of threads that call snet cliente call ... at the same time, just a few (like 3/10) got a response. All the others 7/10 will output this ERROR:

...
requests.exceptions.HTTPError: 429 Client Error: Too Many Requests for url: https://ropsten.infura.io/

So I think that this huge delay and error are coming from interaction with the Blockchain (for some validations).
So this is "blocking" a concise load test, that should involve the snet-cli and snetd without blockchain.