common-config.yml should not be required to be first element of VarFiles

[yngvark]

... for schema config and migration to work.

Description

If package.yml does this:

    - OutputFolder: app-common
      Template: app-common
      Ref: app-common-v3.1.3
      VarFiles:
        - _config/app-hello.yml
        - _config/common-config.yml

instead of this:

    - OutputFolder: app-common
      Template: app-common
      Ref: app-common-v3.1.3
      VarFiles:
        - _config/common-config.yml
        - _config/app-hello.yml

then ok thinks common-config.yml is an app config.

Figure out how to deal with this

Motivation

More robustness.f