Handle simple glob patterns when upgrading the sync patterns

[corneliusweig]

Also simple glob patterns are flattened at the destination. The translation to the new sync config was not handled correctly for cases such as:

- public/*: /app/public
- public/index.html: /app/public

---

Now, for compatible source patterns, the strip field is correctly populated. For example:
IN:

apiVersion: skaffold/v1beta8
kind: Config
build:
  artifacts:
  - image: myimage
    sync:
      public/*: /app/public

OUT (skaffold fix):

apiVersion: skaffold/v1beta11
kind: Config
build:
  artifacts:
  - image: myimage
    sync:
      manual:
      - src: public/*
        dest: /app/

This requires also a simplification of the sync rule, if strip is a suffix of dest, which is now also applied to triple-star patterns.

Fix #2280

[dgageot]

@corneliusweig you have a linter error: https://travis-ci.org/GoogleContainerTools/skaffold/jobs/547387037#L555

[corneliusweig]

Whoops o_O .. fixed