Some exceptions raise UnicodeError

Use utils.exception_to_str to consistently cast the
exception to avoid the unicodeError stack trace.

Closes-Bug: #1340002
Related-Id: I54fce91c73adca846ec99ed50a57b95d16428ec1

Change-Id: I77478a8eeeefd85bf98138156429df53d0a4c079
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Merge "Some exceptions raise UnicodeError"