Add powershell to /etc/shells (#1939)
Add powershell to /etc/shells (#1939)

Manages /etc/shells with after (un)install scripts for CentOS and Ubuntu

Fixes #1913
KarolKaczmarek/PowerShell,jsoref/PowerShell,JamesWTruher/PowerShell-1,TravisEz13/PowerShell,daxian-dbw/PowerShell,KarolKaczmarek/PowerShell,daxian-dbw/PowerShell,bmanikm/PowerShell,jsoref/PowerShell,PaulHigin/PowerShell,bmanikm/PowerShell,bingbing8/PowerShell,jsoref/PowerShell,PaulHigin/PowerShell,bmanikm/PowerShell,JamesWTruher/PowerShell-1,bingbing8/PowerShell,KarolKaczmarek/PowerShell,PaulHigin/PowerShell,JamesWTruher/PowerShell-1,PaulHigin/PowerShell,bingbing8/PowerShell,KarolKaczmarek/PowerShell,TravisEz13/PowerShell,jsoref/PowerShell,bmanikm/PowerShell,bingbing8/PowerShell,JamesWTruher/PowerShell-1,KarolKaczmarek/PowerShell,TravisEz13/PowerShell,bmanikm/PowerShell,jsoref/PowerShell,bingbing8/PowerShell,TravisEz13/PowerShell,daxian-dbw/PowerShell,daxian-dbw/PowerShell