Display hiera values for `vagrant hiera <key>`
Display hiera values for `vagrant hiera <key>`

More intuitive as most configuration commands work this way.

Also change the help text a bit to make it clearer that it will
only display overrides that have been set the same way, not hiera
values in general.

Change-Id: Icf750331b673a9033042c11168251e5121167817

wikimedia/mediawiki-vagrant,wikimedia/mediawiki-vagrant,wikimedia/mediawiki-vagrant,wikimedia/mediawiki-vagrant,wikimedia/mediawiki-vagrant,wikimedia/mediawiki-vagrant