fixes #6381 - properly calculate pxe image urls when using content
refs #6381 - changing validate_media? override to alias chain

also removing the use of eval
Fixes #6366/BZ1112865 - restore readonly product functionality.

When replacing the authorization system we removed the logic
that determines whether or not a product is read only.  This commit
restores that logic.
Merge pull request #4347 from jlsherrill/ohadlevy-4341-2

fixes #6381 - properly calculate pxe image urls when using capsule content
Fixes #6347 - AK doc add/rm_host_coll BZ1101537

Fix the http actions documented for add_host_collections and
remove_host_collections.
Merge pull request #4343 from waldenraines/6366

Fixes #6366/BZ1112865 - restore readonly product functionality.
Merge pull request #4332 from dustint-rh/AK_add_host_collections

Fixes #6347 - AK doc add/rm_host_coll BZ1101537