core: print environment diff based on str conversion

enable detect complex object modification within environment, such as
lists.

Change-Id: I15969681d8fab57e326a7977a5ed0703d4e9fbd7
Signed-off-by: Yedidyah Bar David <didi@redhat.com>
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>