Add an argparse abbreviated mode to --failfast
Add an argparse abbreviated mode to --failfast

Short options should only be a single character. If not, they can't be
concatenated in a single "-word" (from review by luke-jr).

F is chosen instead of f, because f could be reserved to the nested
wallet_hd.py (test_framework/test_framework.py) arguments parser.

Xekyo/bitcoin,mruddy/bitcoin,domob1812/namecore,achow101/bitcoin,namecoin/namecore,GroestlCoin/bitcoin,fanquake/bitcoin,prusnak/bitcoin,AkioNak/bitcoin,mruddy/bitcoin,domob1812/bitcoin,fujicoin/fujicoin,jamesob/bitcoin,MarcoFalke/bitcoin,Xekyo/bitcoin,mm-s/bitcoin,bitcoinknots/bitcoin,domob1812/namecore,GroestlCoin/GroestlCoin,bitcoinknots/bitcoin,kallewoof/bitcoin,MarcoFalke/bitcoin,achow101/bitcoin,jlopp/statoshi,GroestlCoin/GroestlCoin,sstone/bitcoin,namecoin/namecoin-core,jambolo/bitcoin,jamesob/bitcoin,namecoin/namecore,instagibbs/bitcoin,tecnovert/particl-core,namecoin/namecoin-core,ajtowns/bitcoin,instagibbs/bitcoin,ajtowns/bitcoin,andreaskern/bitcoin,prusnak/bitcoin,mm-s/bitcoin,namecoin/namecoin-core,GroestlCoin/GroestlCoin,AkioNak/bitcoin,namecoin/namecore,jlopp/statoshi,jlopp/statoshi,dscotese/bitcoin,tecnovert/particl-core,achow101/bitcoin,mm-s/bitcoin,fanquake/bitcoin,MarcoFalke/bitcoin,ajtowns/bitcoin,fanquake/bitcoin,sipsorcery/bitcoin,mruddy/bitcoin,sstone/bitcoin,domob1812/bitcoin,MarcoFalke/bitcoin,AkioNak/bitcoin,namecoin/namecoin-core,lateminer/bitcoin,pataquets/namecoin-core,kallewoof/bitcoin,sstone/bitcoin,pataquets/namecoin-core,anditto/bitcoin,namecoin/namecore,jlopp/statoshi,bitcoin/bitcoin,achow101/bitcoin,lateminer/bitcoin,bitcoinsSG/bitcoin,bitcoinknots/bitcoin,fanquake/bitcoin,AkioNak/bitcoin,sipsorcery/bitcoin,domob1812/bitcoin,jambolo/bitcoin,sipsorcery/bitcoin,lateminer/bitcoin,domob1812/bitcoin,sstone/bitcoin,kallewoof/bitcoin,jamesob/bitcoin,instagibbs/bitcoin,jambolo/bitcoin,dscotese/bitcoin,fanquake/bitcoin,GroestlCoin/bitcoin,domob1812/namecore,MarcoFalke/bitcoin,sipsorcery/bitcoin,andreaskern/bitcoin,particl/particl-core,Xekyo/bitcoin,GroestlCoin/bitcoin,mruddy/bitcoin,GroestlCoin/bitcoin,GroestlCoin/bitcoin,ajtowns/bitcoin,particl/particl-core,dscotese/bitcoin,tecnovert/particl-core,bitcoinsSG/bitcoin,andreaskern/bitcoin,lateminer/bitcoin,kallewoof/bitcoin,particl/particl-core,GroestlCoin/GroestlCoin,andreaskern/bitcoin,kallewoof/bitcoin,andreaskern/bitcoin,bitcoin/bitcoin,jambolo/bitcoin,jlopp/statoshi,fujicoin/fujicoin,fujicoin/fujicoin,achow101/bitcoin,namecoin/namecoin-core,ajtowns/bitcoin,fanquake/bitcoin,GroestlCoin/GroestlCoin,domob1812/bitcoin,bitcoinknots/bitcoin,bitcoin/bitcoin,namecoin/namecore,bitcoinknots/bitcoin,GroestlCoin/GroestlCoin,prusnak/bitcoin,sipsorcery/bitcoin,achow101/bitcoin,particl/particl-core,jamesob/bitcoin,instagibbs/bitcoin,prusnak/bitcoin,jlopp/statoshi,prusnak/bitcoin,mruddy/bitcoin,fujicoin/fujicoin,andreaskern/bitcoin,pataquets/namecoin-core,anditto/bitcoin,tecnovert/particl-core,AkioNak/bitcoin,pataquets/namecoin-core,anditto/bitcoin,mruddy/bitcoin,jambolo/bitcoin,Xekyo/bitcoin,domob1812/namecore,Xekyo/bitcoin,jambolo/bitcoin,anditto/bitcoin,namecoin/namecore,jamesob/bitcoin,bitcoin/bitcoin,domob1812/namecore,anditto/bitcoin,bitcoinsSG/bitcoin,kallewoof/bitcoin,tecnovert/particl-core,instagibbs/bitcoin,anditto/bitcoin,mm-s/bitcoin,fujicoin/fujicoin,sipsorcery/bitcoin,AkioNak/bitcoin,sstone/bitcoin,MarcoFalke/bitcoin,jamesob/bitcoin,bitcoinsSG/bitcoin,mm-s/bitcoin,pataquets/namecoin-core,fujicoin/fujicoin,particl/particl-core,dscotese/bitcoin,GroestlCoin/bitcoin,dscotese/bitcoin,bitcoinsSG/bitcoin,domob1812/namecore,lateminer/bitcoin,bitcoinsSG/bitcoin,instagibbs/bitcoin,pataquets/namecoin-core,tecnovert/particl-core,bitcoin/bitcoin,lateminer/bitcoin,particl/particl-core,bitcoin/bitcoin,domob1812/bitcoin,ajtowns/bitcoin,mm-s/bitcoin,Xekyo/bitcoin,dscotese/bitcoin,prusnak/bitcoin,sstone/bitcoin,namecoin/namecoin-core