Add test for detecting shell when `rbenv init` is called from script
Add test for detecting shell when `rbenv init` is called from script

References #730

cehoffman/nodenv,sstephenson/rbenv,OiNutter/nodenv,zmwangx/pyenv,docwhat/rbenv,jasonkarns/rbenv,Angeldude/rbenv,jeremy/rbenv,sstephenson/rbenv,sstephenson/rbenv,pyenv/pyenv,yyyc514/rbenv,syndbg/goenv,jasonkarns/rbenv,yyuu/pyenv,syndbg/goenv,cehoffman/rbenv,sebhahn/pyenv,viclim/rbenv,yyyc514/rbenv,docwhat/rbenv,pyenv/pyenv,cehoffman/pyenv,genome-vendor/pyenv,jrolfs/nodenv,viclim/rbenv,Angeldude/rbenv,jeremy/rbenv,Angeldude/rbenv,BanzaiMan/pyenv,nodenv/nodenv,zmwangx/pyenv,cehoffman/rbenv,yyyc514/rbenv,jeremy/rbenv,syndbg/goenv,cehoffman/nodenv,syndbg/goenv,pyenv/pyenv,yyuu/pyenv,cehoffman/rbenv,rbenv/rbenv,sebhahn/pyenv,jasonkarns/rbenv,OiNutter/nodenv,rbenv/rbenv,viclim/rbenv,genome-vendor/pyenv,jrolfs/nodenv,nodenv/nodenv,BanzaiMan/pyenv,cehoffman/pyenv,sebhahn/pyenv,docwhat/rbenv