Refactor: tools: New instruction message in crm_shadow

We need a way to give the user instructions via XML output. out->info()
won't work since that method isn't implemented for XML.

This commit introduces a simple "instruction" message function. The
default is to simply call out->info(). For XML output, we create a text
node under an <instruction> element.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>