packages: Adding new functions
packages: Adding new functions

This patch add three new methods :
- is_package_installed : return if the requested package is already
  installed
- rebuild_db : rebuild the package database from inside the chroot
- rebuild_db_with_local: rebuild the package database from the host

The two rebuild_db calls are needed with using RPM based distro.
When performing updates on a target, the rpm format could be different
from outside & inside the chroot.

redhat-cip/edeploy,lebauce/edeploy,lebauce/edeploy,redhat-cip/edeploy,redhat-cip/edeploy,redhat-cip/edeploy,enovance/edeploy,enovance/edeploy,lebauce/edeploy,enovance/edeploy,lebauce/edeploy,enovance/edeploy