Fixed incorrect exception type on deserializer lookup

 - removed .toString() call from log
 - updated test to match functionality
 - lowered log level on (de)serializer overwriting

Change-Id: Ie58dc4e4d9bac76532a4df55170ed52e0a0e5fbc
Signed-off-by: Michal Polkorab <michal.polkorab@pantheon.sk>