tests: for bitcoin.py, added new ones, and some refactoring for existing
tests: for bitcoin.py, added new ones, and some refactoring for existing

new ones mainly include:
- privkey -> pubkey -> addr conversions
- xprv, xpub operations

dabura667/electrum,neocogent/electrum,asfin/electrum,neocogent/electrum,asfin/electrum,fyookball/electrum,pooler/electrum-ltc,kyuupichan/electrum,romanz/electrum,fujicoin/electrum-fjc,spesmilo/electrum,cryptapus/electrum,cryptapus/electrum,dabura667/electrum,cryptapus/electrum,spesmilo/electrum,dabura667/electrum,fyookball/electrum,dabura667/electrum,kyuupichan/electrum,asfin/electrum,vialectrum/vialectrum,kyuupichan/electrum,neocogent/electrum,fujicoin/electrum-fjc,spesmilo/electrum,digitalbitbox/electrum,wakiyamap/electrum-mona,digitalbitbox/electrum,pooler/electrum-ltc,wakiyamap/electrum-mona,fujicoin/electrum-fjc,wakiyamap/electrum-mona,romanz/electrum,digitalbitbox/electrum,vialectrum/vialectrum,fyookball/electrum,romanz/electrum,vialectrum/vialectrum,pooler/electrum-ltc,pooler/electrum-ltc,wakiyamap/electrum-mona,spesmilo/electrum,digitalbitbox/electrum