boneyard-formula-pr: add local-only mode
boneyard-formula-pr: add local-only mode

Allow boneyarding a formula locally, i.e. make all the necessary changes
in the local repositories but don't push them to a remote and don't open
a pull request automatically.

gordonmcshane/homebrew,alyssais/brew,toonetown/homebrew,DomT4/brew,bfontaine/brew,Homebrew/brew,mahori/brew,maxim-belkin/brew,claui/brew,rwhogg/brew,aw1621107/brew,DomT4/brew,ilovezfs/brew,Linuxbrew/brew,Linuxbrew/brew,palxex/brew,zmwangx/brew,ilovezfs/brew,JCount/brew,reitermarkus/brew,AnastasiaSulyagina/brew,bfontaine/brew,mgrimes/brew,sjackman/homebrew,JCount/brew,muellermartin/dist,gregory-nisbet/brew,hanxue/linuxbrew,bfontaine/brew,hanxue/linuxbrew,reelsense/brew,tonyg/homebrew,hanxue/linuxbrew,EricFromCanada/brew,jmsundar/brew,Homebrew/brew,vitorgalvao/brew,tonyg/homebrew,muellermartin/dist,amar-laksh/brew_sudo,toonetown/homebrew,palxex/brew,Homebrew/brew,zmwangx/brew,nandub/brew,EricFromCanada/brew,vitorgalvao/brew,nandub/brew,reitermarkus/brew,alyssais/brew,maxim-belkin/brew,AnastasiaSulyagina/brew,rwhogg/brew,konqui/brew,mahori/brew,pseudocody/brew,aw1621107/brew,maxim-belkin/brew,gregory-nisbet/brew,nandub/brew,reitermarkus/brew,JCount/brew,MikeMcQuaid/brew,claui/brew,reelsense/brew,AnastasiaSulyagina/brew,sjackman/homebrew,DomT4/brew,pseudocody/brew,tonyg/homebrew,muellermartin/dist,Homebrew/brew,vitorgalvao/brew,jmsundar/brew,EricFromCanada/brew,MikeMcQuaid/brew,claui/brew,ilovezfs/brew,palxex/brew,pseudocody/brew,zmwangx/brew,amar-laksh/brew_sudo,gregory-nisbet/brew,MikeMcQuaid/brew,reelsense/brew,mahori/brew,mahori/brew,sjackman/homebrew,konqui/brew,toonetown/homebrew,jmsundar/brew,mgrimes/brew,EricFromCanada/brew,Linuxbrew/brew,reitermarkus/brew,gordonmcshane/homebrew,aw1621107/brew,vitorgalvao/brew,DomT4/brew,JCount/brew,gordonmcshane/homebrew,sjackman/homebrew,Linuxbrew/brew,nandub/brew,rwhogg/brew,claui/brew,MikeMcQuaid/brew,mgrimes/brew,amar-laksh/brew_sudo,alyssais/brew,konqui/brew,konqui/brew