416543 Add correct p2-artifacts.properties entry for remote artifacts

- Add correct entry to p2-artifacts.properties in case an artifact plus
  its p2Metadata.xml and p2Artifacts.xml is downloaded from a remote
  Maven repository.

Bug: 416543
Bug: 352154
Change-Id: If3ed6742e8d254a9fac01df3ca9481daead558a9