Disable entropy capture if parameter ?testnet=true is set

[felipelalli]

Or at least decrease the amount to be collected. I am developing a system in testnet and this entropy collection is really annoying. Testnet wallet is not so critical.

[cantonbecker]

Or, another option would be to add a "skip" option. Example:

https://bitcoinpaperwallet.com/bitcoinpaperwallet/generate-wallet.html

This is also handy for folks who are using the software just to check an existing key, decrypt something from BIP38, etc.

I'd submit a pull request but this is one of those areas where my own code has diverged a bit too much from bitaddress.org to be directly useful.