#538 shutdown the `OracleAgent` at `VaultService` level

[b-yap]

Addresses #538.

In the logs, the try_shutdown_wallet() logs just fine, so I plan to do the same thing for OracleAgent. To do this, the agent has to be accessible at the VaultService level. So I added anagent field in VaultService.

I removed subscription of the ShutdownSender because of its erratic behavior in the OracleAgent; sometimes it works, sometimes it doesn't.

[b-yap]

fetch_transactions_iter_success is failing on testnet. I changed to Public network, and it ran just fine. :no_mouth:

[ebma]

You tested that change locally @b-yap? How annoying.

[b-yap]

@ebma Yes I tested it locally, but analyzed and found faults in the code, so I updated it. :+1: