try and add some consistency with the show and delete commands.
replace 'show x' with 'display x'
change 'delete a y' with just 'delete y'
Change-Id: I47dfa8ee23ac5c41b355796415eb515155832f65
Also tweaked the code for `mapping set` as it was previously
using cliff Show instead of cliff Command.
Change-Id: I0ea1383a9f2dddf4b2f717b2aa16bbd60ab1720c