upgrade-scripts: Fix to invoke as an error when untar fails

upgrade-scripts: Fix to invoke as an error when untar fails

Previously, if the untaring of any delta file from the delta.tar.gz
fails, then the script ignored it and continued to the next delta file.
This may cause some delta files to be not applied which causes the
failure of the FOTA as a result.
To prevent this, the log message was changed to 'Error' from 'Info" and
'exit_error' was used instead of 'continue'.

Change-Id: Idffe1387a58b9a358f717bae4a334405b8946da4
Signed-off-by: SangYoun Kwak <sy.kwak@samsung.com>