Trust but verify 'scutil' to return ComputerName
Trust but verify 'scutil' to return ComputerName

Apparently, it is possible to set up a Mac such that
`scutil --get ComputerName` hasn't been set.

This change checks if that fails and falls back to the original
mechanism.

Closes #2155
Closes #2183

hbpoison/oh-my-zsh,hbpoison/oh-my-zsh,hbpoison/oh-my-zsh,hbpoison/oh-my-zsh