Move cli generated files out of common

There's no shared usage for these files, so move them into a
subdirectory of cli-reference.

Call the subdirectory generated and add a README so that it's clear that
these are generated files.

Fix also .gitignore to only ignore some top-level directories.

Change-Id: Ifb455a8640cc7e735ed81563b438d68522e73ded
Merge "Move cli generated files out of common"