util: Simplify path argument for CBlockTreeDB ctor
util: Simplify path argument for CBlockTreeDB ctor

This commit does not change behavior as GetBlocksDir() with unset 
"-blocksdir" returns the same path.

bitcoinknots/bitcoin,monacoinproject/monacoin,gjhiggins/vcoincore,namecoin/namecoin-core,domob1812/bitcoin,sstone/bitcoin,rnicoll/bitcoin,JeremyRubin/bitcoin,fujicoin/fujicoin,Sjors/bitcoin,Sjors/bitcoin,achow101/bitcoin,peercoin/peercoin,sstone/bitcoin,mruddy/bitcoin,midnightmagic/bitcoin,JeremyRubin/bitcoin,rnicoll/bitcoin,jnewbery/bitcoin,particl/particl-core,dscotese/bitcoin,GroestlCoin/bitcoin,tecnovert/particl-core,apoelstra/bitcoin,kallewoof/bitcoin,pstratem/bitcoin,pataquets/namecoin-core,MeshCollider/bitcoin,rnicoll/bitcoin,apoelstra/bitcoin,ElementsProject/elements,vertcoin/vertcoin,monacoinproject/monacoin,lateminer/bitcoin,tjps/bitcoin,jlopp/statoshi,pataquets/namecoin-core,instagibbs/bitcoin,kallewoof/bitcoin,rnicoll/bitcoin,Xekyo/bitcoin,pataquets/namecoin-core,apoelstra/bitcoin,jtimon/bitcoin,dscotese/bitcoin,practicalswift/bitcoin,MeshCollider/bitcoin,andreaskern/bitcoin,pstratem/bitcoin,alecalve/bitcoin,mruddy/bitcoin,n1bor/bitcoin,domob1812/namecore,n1bor/bitcoin,mruddy/bitcoin,mm-s/bitcoin,ElementsProject/elements,DigitalPandacoin/pandacoin,namecoin/namecoin-core,Xekyo/bitcoin,cdecker/bitcoin,cdecker/bitcoin,domob1812/namecore,andreaskern/bitcoin,fanquake/bitcoin,namecoin/namecoin-core,GroestlCoin/bitcoin,bitcoin/bitcoin,practicalswift/bitcoin,qtumproject/qtum,GroestlCoin/GroestlCoin,gjhiggins/vcoincore,tjps/bitcoin,andreaskern/bitcoin,Sjors/bitcoin,kallewoof/bitcoin,ajtowns/bitcoin,dscotese/bitcoin,lateminer/bitcoin,particl/particl-core,tecnovert/particl-core,jamesob/bitcoin,bitcoinsSG/bitcoin,GroestlCoin/GroestlCoin,gjhiggins/vcoincore,bitcoin/bitcoin,tjps/bitcoin,jtimon/bitcoin,mruddy/bitcoin,alecalve/bitcoin,ElementsProject/elements,qtumproject/qtum,prusnak/bitcoin,gjhiggins/vcoincore,Xekyo/bitcoin,MarcoFalke/bitcoin,tecnovert/particl-core,yenliangl/bitcoin,kallewoof/bitcoin,tecnovert/particl-core,cdecker/bitcoin,sipsorcery/bitcoin,mitchellcash/bitcoin,AkioNak/bitcoin,MarcoFalke/bitcoin,particl/particl-core,sstone/bitcoin,jambolo/bitcoin,alecalve/bitcoin,tjps/bitcoin,EthanHeilman/bitcoin,rnicoll/dogecoin,lateminer/bitcoin,achow101/bitcoin,DigitalPandacoin/pandacoin,andreaskern/bitcoin,fujicoin/fujicoin,jamesob/bitcoin,practicalswift/bitcoin,mm-s/bitcoin,vertcoin/vertcoin,ajtowns/bitcoin,kallewoof/bitcoin,anditto/bitcoin,sstone/bitcoin,domob1812/bitcoin,jamesob/bitcoin,anditto/bitcoin,GroestlCoin/GroestlCoin,prusnak/bitcoin,fanquake/bitcoin,instagibbs/bitcoin,jamesob/bitcoin,practicalswift/bitcoin,mm-s/bitcoin,ahmedbodi/vertcoin,ajtowns/bitcoin,fujicoin/fujicoin,jonasschnelli/bitcoin,EthanHeilman/bitcoin,DigitalPandacoin/pandacoin,EthanHeilman/bitcoin,sstone/bitcoin,GroestlCoin/bitcoin,ahmedbodi/vertcoin,andreaskern/bitcoin,apoelstra/bitcoin,jtimon/bitcoin,ajtowns/bitcoin,sipsorcery/bitcoin,jambolo/bitcoin,AkioNak/bitcoin,alecalve/bitcoin,Sjors/bitcoin,achow101/bitcoin,jambolo/bitcoin,particl/particl-core,bitcoinknots/bitcoin,rnicoll/dogecoin,mruddy/bitcoin,rnicoll/dogecoin,instagibbs/bitcoin,ahmedbodi/vertcoin,practicalswift/bitcoin,AkioNak/bitcoin,achow101/bitcoin,mruddy/bitcoin,ElementsProject/elements,namecoin/namecoin-core,AkioNak/bitcoin,vertcoin/vertcoin,ahmedbodi/vertcoin,DigitalPandacoin/pandacoin,alecalve/bitcoin,domob1812/namecore,bitcoinknots/bitcoin,mitchellcash/bitcoin,bitcoinknots/bitcoin,domob1812/bitcoin,monacoinproject/monacoin,midnightmagic/bitcoin,tjps/bitcoin,bitcoin/bitcoin,MarcoFalke/bitcoin,jtimon/bitcoin,bitcoinsSG/bitcoin,prusnak/bitcoin,n1bor/bitcoin,jnewbery/bitcoin,midnightmagic/bitcoin,rnicoll/bitcoin,monacoinproject/monacoin,litecoin-project/litecoin,jonasschnelli/bitcoin,peercoin/peercoin,gjhiggins/vcoincore,fujicoin/fujicoin,qtumproject/qtum,JeremyRubin/bitcoin,peercoin/peercoin,mm-s/bitcoin,lateminer/bitcoin,yenliangl/bitcoin,fujicoin/fujicoin,ahmedbodi/vertcoin,EthanHeilman/bitcoin,GroestlCoin/GroestlCoin,sipsorcery/bitcoin,rnicoll/bitcoin,litecoin-project/litecoin,namecoin/namecore,namecoin/namecoin-core,prusnak/bitcoin,jnewbery/bitcoin,jonasschnelli/bitcoin,apoelstra/bitcoin,apoelstra/bitcoin,yenliangl/bitcoin,jtimon/bitcoin,litecoin-project/litecoin,fanquake/bitcoin,vertcoin/vertcoin,DigitalPandacoin/pandacoin,peercoin/peercoin,bitcoinknots/bitcoin,yenliangl/bitcoin,qtumproject/qtum,jlopp/statoshi,pstratem/bitcoin,particl/particl-core,achow101/bitcoin,cdecker/bitcoin,domob1812/namecore,jlopp/statoshi,dscotese/bitcoin,fanquake/bitcoin,midnightmagic/bitcoin,sipsorcery/bitcoin,n1bor/bitcoin,anditto/bitcoin,ElementsProject/elements,GroestlCoin/bitcoin,qtumproject/qtum,namecoin/namecoin-core,GroestlCoin/GroestlCoin,dscotese/bitcoin,jonasschnelli/bitcoin,Xekyo/bitcoin,mitchellcash/bitcoin,anditto/bitcoin,ahmedbodi/vertcoin,domob1812/bitcoin,rnicoll/dogecoin,particl/particl-core,kallewoof/bitcoin,jamesob/bitcoin,namecoin/namecore,jambolo/bitcoin,MeshCollider/bitcoin,EthanHeilman/bitcoin,domob1812/bitcoin,cdecker/bitcoin,prusnak/bitcoin,alecalve/bitcoin,n1bor/bitcoin,cdecker/bitcoin,mm-s/bitcoin,EthanHeilman/bitcoin,JeremyRubin/bitcoin,jtimon/bitcoin,fanquake/bitcoin,yenliangl/bitcoin,midnightmagic/bitcoin,qtumproject/qtum,Xekyo/bitcoin,instagibbs/bitcoin,fanquake/bitcoin,instagibbs/bitcoin,rnicoll/dogecoin,pstratem/bitcoin,AkioNak/bitcoin,mitchellcash/bitcoin,JeremyRubin/bitcoin,MarcoFalke/bitcoin,jambolo/bitcoin,peercoin/peercoin,tecnovert/particl-core,ElementsProject/elements,MeshCollider/bitcoin,n1bor/bitcoin,anditto/bitcoin,vertcoin/vertcoin,tjps/bitcoin,MarcoFalke/bitcoin,jlopp/statoshi,jlopp/statoshi,pataquets/namecoin-core,jnewbery/bitcoin,pstratem/bitcoin,pstratem/bitcoin,sipsorcery/bitcoin,sstone/bitcoin,namecoin/namecore,ajtowns/bitcoin,bitcoinsSG/bitcoin,jamesob/bitcoin,mitchellcash/bitcoin,MarcoFalke/bitcoin,qtumproject/qtum,vertcoin/vertcoin,bitcoin/bitcoin,bitcoin/bitcoin,sipsorcery/bitcoin,domob1812/namecore,Sjors/bitcoin,bitcoinsSG/bitcoin,jambolo/bitcoin,domob1812/bitcoin,ajtowns/bitcoin,AkioNak/bitcoin,Xekyo/bitcoin,GroestlCoin/GroestlCoin,litecoin-project/litecoin,jnewbery/bitcoin,fujicoin/fujicoin,jlopp/statoshi,anditto/bitcoin,gjhiggins/vcoincore,pataquets/namecoin-core,JeremyRubin/bitcoin,achow101/bitcoin,lateminer/bitcoin,bitcoin/bitcoin,prusnak/bitcoin,namecoin/namecore,instagibbs/bitcoin,dscotese/bitcoin,monacoinproject/monacoin,GroestlCoin/bitcoin,monacoinproject/monacoin,GroestlCoin/bitcoin,pataquets/namecoin-core,midnightmagic/bitcoin,namecoin/namecore,lateminer/bitcoin,yenliangl/bitcoin,jonasschnelli/bitcoin,domob1812/namecore,tecnovert/particl-core,peercoin/peercoin,litecoin-project/litecoin,practicalswift/bitcoin,litecoin-project/litecoin,mitchellcash/bitcoin,namecoin/namecore,MeshCollider/bitcoin,bitcoinsSG/bitcoin,andreaskern/bitcoin,bitcoinsSG/bitcoin,DigitalPandacoin/pandacoin,mm-s/bitcoin,MeshCollider/bitcoin