Use env to store private keys, mnemonic and keystore in tests folder

[EnoRage]

Here you can see mnemonic: https://github.com/binance-chain/javascript-sdk/blob/master/tests/client.test.js#L7

I found some money on this mnemonic on mainnet too. Is it there for specific purpose?)

[notatestuser]

Ha, funny to see that it has a few cents on the mainnet.. not sure how that happened. However, we use this mnemonic for some end-to-end tests.

Thanks for pointing this out - it should really be stored in an environment variable or something.