lib/oe/package_manager.py: add new package management library

lib/oe/package_manager.py: add new package management library

This new library is intended to be used by the new python rootfs
creation code.

It implements the rpm/dpkg/opkg package management backends: RpmPM,
DpkgPM and OpkgPM.

The base API is this:
  update()
  install()
  install_complementary()
  remove()
  write_index()
  remove_packaging_data()
  list_installed()

All implementations have to provide these functions. Some backends may
need to implement additional functions though.

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>