Supoort new repos.yaml format in backenddb

Supoort new repos.yaml format in backenddb

To support merge multiply repos into one single snapshot,
add new keyword'Targets' in repos.yaml and remove origin 'Target'.
One example shows asbelow.
- Name: Tizen-generic
  Link: latest
  Release: "tizen"
  TopLevel: /srv/builds/temp/generic
  Project: Tizen:Generic
  ProjectConfig: yes
  SnapshotDir: snapshots/tizen/generic/
  PrereleaseDir: prerelease/tizen/generic/
  Targets:
      - Name: ia32-wayland
        Architectures:
            - ia32
      - Name: ia32-x11
        Architectures:
            - ia32

Fixes: #1820

Change-Id: I81adb4e9333b770e119755168a79400b91cee262