fix #5 - Breaks when a Package title != name

[giuliano108]

I can't open an upstream PR because fix_tests hasn't been merged yet...

This PR should address bug #5. Please have a look there for context.

In summary: when computing the set of managed packages, we can't just look them up by title in the Catalog. Because title and name can be different, we need to look into the "resource aliases" table too.

package {'arbitrarytitle': name => 'pkgname'}

I couldn't find a public API to access @aliases, hence the instance_variable_get hack... :(

/cc @hashbrowncipher @solarkennedy @oholiab

[giuliano108]

In the last commit I've collapsed everything down to:

catalog_r = catalog.resource(r.ref) || find_resource_alias(["Package", r.name, :held_apt])

Is that any better?

[giuliano108]

#2 , which I just merged, also includes this.