Schemas: Slightly simplify mode regexp

Slightly simplify "mode" attribute regexp in schemas for "config_files"
and "changed_managed_files" scopes.
Schemas: Fix indentation

Fix indentation in schemas for "config_files" and
"changed_managed_files" scopes.
Schemas: Improve definition names

Change definition names in schemas for "config_files" and
"changed_managed_files" scopes. The new names better describe what the
definitions represent.
Merge pull request #180 from SUSE/schema-config-files-changed-managed-files-tweaks

[Review] Request from 'dmajda' @ 'SUSE/machinery/schema-config-files-changed-managed-files-tweaks'
Use SystemDescriptionStore to load validation file

Showing the file path requires the SystemDescriptionStore object
to check the real error message.

Removed unnecessary unit test due to other tests validates this.

Moved the validation files to keep uniform direcory layout.

Moved validation tests from system_description_spec to
system_description_validation_spec.
Consolidate integration validation descriptions with unit tests

Moved the integration invalid-json and validation-errors into
subdirectorys to have the same layout as the unit tests.
Add file path to validation error message
Move validate task descriptions to common directory