core: Added log when retrieving entities from tar

Adding a log for the retrieve of entities process so it will be easier
to understand the flow through the engine log file.

Bug-Url: https://bugzilla.redhat.com/1119376
Change-Id: I11b1102b64c6951376a5242364435515b41d24fb
Signed-off-by: Maor Lipchuk <mlipchuk@redhat.com>