config: backup when current config is different from recent backup copy
config: backup when current config is different from recent backup copy

With this change,
when '/etc/target/saveconfig.json' is same as '/etc/target/backup/saveconfig-${latest-stamp}.json
we skip backing up saveconfig.json

Signed-off-by: Prasanna Kumar Kalever <a78d8f98557446023f5b3ba9944d7be259a978a3@redhat.com>

cvubrugier/targetcli-fb,agrover/targetcli-fb