Schemas: Remove duplication

Remove duplicate property schemas in schemas for "config_files" and
"changed_managed_files" scopes.
Schemas: More precise descriptions of file states

In case of "config_files" and "changed_managed_files" scopes, there are
two possible states of each file:

  1. The file was changed ("status": "changed")

     This state has two sub-states:

     1.1 The file was modified ("changes": [...]).

         In this case, the list of changes is saved in the "changes"
         attribute and file metadata is saved in the "mode", "user" and
         "group" attributes.

     1.2 The file was deleted ("changes": ["deleted"]).

         In this case, no metadata is saved.

  2. Determining whether the file was changed resulted in an error
     ("status": "error").

     In this case, the error message is saved in the "error_message"
     attribute.

This commit modifies schemas for "config_files" and
"changed_managed_files" scopes to match the states correctly.
Merge pull request #184 from SUSE/schema-config-files-changed-managed-files-more-tweaks

[Review] Request from 'dmajda' @ 'SUSE/machinery/schema-config-files-changed-managed-files-more-tweaks'