Lower log level to warn for handled pack errors

Lower log level to warn for handled pack errors

Pack not found and pack corrupted/invalid are handled by the code (pack
is removed from the list) so logging an error and the stacktrace is
misleading because it implies that there is an action to take to fix the
error.

Lower the log level to warn and remove the stacktrace for those 2 types
of errors and keep the error log statement for any other.

Change-Id: I2400fe5fec07ac6d6c244b852cce615663774e6e
Signed-off-by: Hugo Arès <hugo.ares@ericsson.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>