Improvement: Password input

[philmb3487]

Problem

This PR aims to improve the cli program by bringing in hidden password input.

Root Cause

We don’t want to show passwords in clear text.

Solution

Bring in two commits from Bitcoin upstream.
One introduces the stdin interfaces, the other to patch in -stdin* interfaces.

Unit Testing Results

1. The build is successful.
2. Test veil-cli with the following flags, in random combinations thereof:

→ -stdin
→ -stdinrpcpass
→ -stdinwalletpassphrase

3. Is the behaviour acceptable?

[mimirmim]

Sweet this addresses my issues with #768. I'll give this a test when I wake up.

[codeofalltrades]

ACK 968977f

[CaveSpectre11]

Only problem was the lack of carriage return when using multiple inputs; or seeing the response from an rcp command:

$ ./veil-cli -stdinrpcpass -stdinwalletpassphrase walletpassphrase
RPC password> Wallet passphrase> error code: -1

These have been added:

$ ./veil-cli -stdinrpcpass -stdinwalletpassphrase walletpassphrase
RPC password>
Wallet passphrase>
error: Could not connect to the server

ACK 27e0d2b

@codeofalltrades give it another look please

[seanPhill]

ACK Tested on Win64 build.

veil-cli -testnet -stdinwalletpassphrase walletpassphrase false 10000

This gave a prompt as below, and correctly unlocked the wallet.
Wallet passphrase>

[seanPhill]

C:\Users\me\Veil-Project\veil-pr770> veil-cli -testnet walletlock

C:\Users\me\Veil-Project\veil-pr770> veil-cli -testnet listzerocoinamounts
error code: -13
error message:
Error: Please enter the wallet passphrase with walletpassphrase first.

C:\Users\me\Veil-Project\veil-pr770> veil-cli -testnet -stdinwalletpassphrase walletpassphrase false 10000
Wallet passphrase>

C:\Users\me\Veil-Project\veil-pr770> veil-cli -testnet listzerocoinamounts
[
  {
    "denomination": 10,
    "mints_spendable": 172,
    "mints_pending": 9
  },
  {
    "denomination": 100,
    "mints_spendable": 7,
    "mints_pending": 0
  },
  {
    "denomination": 1000,
    "mints_spendable": 2,
    "mints_pending": 0
  },
  {
    "denomination": 10000,
    "mints_spendable": 0,
    "mints_pending": 0
  }
]