Improve showblock options, add --testnet and change default db to leveldb to match btcd
Improve showblock options, add --testnet and change default db to leveldb
to match btcd

tb00/btcd,soapboxsys/ombfullnode,glv2/ppcd,cjepson/btcd,sysbot/btcd,jcmincke/dcrd,glv2/ppcd,cqswxj2013/btcd,stevenroose/btcd,soapboxsys/ombfullnode,wallclockbuilder/btcd,tb00/btcd,Evil-Coin/Evil,btcsuite/btcd,Cleawing/btcd,danoctavian/btcd,dan-da/btcd,ppcsuite/ppcd-old,Stash-Crypto/btcd,CryptocurrencyCabal/htcd,Roasbeef/btcd,dajohi/btcd,runeaune/btcd,danoctavian/btcd,Evil-Coin/Evil,BitGo/prova,1d4Nf6/btcd,btcsuite/btcd,wallclockbuilder/btcd,ltcsuite/ltcd,aakselrod/btcd,jongillham/btcd,FactomProject/btcd,ppcsuite/ppcd,jrick/dcrd,BitGo/prova,hectorj/btcd,toddfries/btcd,mathiasrw/btcd,jimmysong/btcd,ltcsuite/ltcd,cqswxj2013/btcd,dajohi/btcd,jcmincke/dcrd,davecgh/btcd,pkothbauer/btcd,pkothbauer/btcd,Roasbeef/btcd,Cleawing/btcd,runeaune/btcd,jrick/btcd,ppcsuite/ppcd-old,adiabat/btcd,1d4Nf6/btcd,qchain/btcd,mathiasrw/btcd,Dirbaio/btcd,decred/dcrd,DanielKrawisz/btcd,dajohi/btcd,jimmysong/btcd,toddfries/btcd,ppcsuite/ppcd,jongillham/btcd,jrick/dcrd,aakselrod/btcd,davecgh/btcd,CryptocurrencyCabal/htcd,hectorj/btcd,jcmincke/dcrd,jrick/btcd,dan-da/btcd,btcsuitereleases/btcd,btcsuitereleases/btcd,FactomProject/btcd,Dirbaio/btcd,adiabat/btcd,decred/dcrd,jrick/btcd,Dirbaio/btcd,sysbot/btcd,cjepson/btcd,DanielKrawisz/btcd,stevenroose/btcd,Stash-Crypto/btcd,qchain/btcd