Fix Windows host file modification

[Iristyle]

• Commit 250fad54d4851c0e853c4a38a49fb9e484f5d5f5 introduced using an elevated shell so that a file would be written instead of simply executing these commands. Unfortunately, :elevated => true doesn't seem to currently work properly on Windows with Vagrant 1.6.5 so let's revert that change.
• The original idea behind the prior commit was to workaround script length limitations that may prevent all hosts from being registered properly, so in keeping with that spirit, refactor the PowerShell code to be a shorter one-liner that uses PowerShell constructs to remove repetitive code.