Fix Start-Process Pester tests
Fix Start-Process Pester tests

These tests attempted to stop the test ping process by name, which was
fragile. Now they stop by PID, which is far less fragile.

jsoref/PowerShell,PaulHigin/PowerShell,jsoref/PowerShell,PaulHigin/PowerShell,KarolKaczmarek/PowerShell,JamesWTruher/PowerShell-1,TravisEz13/PowerShell,TravisEz13/PowerShell,JamesWTruher/PowerShell-1,TravisEz13/PowerShell,JamesWTruher/PowerShell-1,kmosher/PowerShell,JamesWTruher/PowerShell-1,KarolKaczmarek/PowerShell,kmosher/PowerShell,daxian-dbw/PowerShell,daxian-dbw/PowerShell,kmosher/PowerShell,KarolKaczmarek/PowerShell,bingbing8/PowerShell,jsoref/PowerShell,TravisEz13/PowerShell,PaulHigin/PowerShell,bingbing8/PowerShell,kmosher/PowerShell,KarolKaczmarek/PowerShell,bingbing8/PowerShell,daxian-dbw/PowerShell,PaulHigin/PowerShell,bmanikm/PowerShell,bingbing8/PowerShell,kmosher/PowerShell,bmanikm/PowerShell,bmanikm/PowerShell,bingbing8/PowerShell,daxian-dbw/PowerShell,bmanikm/PowerShell,bmanikm/PowerShell,jsoref/PowerShell,jsoref/PowerShell,KarolKaczmarek/PowerShell