Accept translated exceptions in exceptions.handle

If an exception with a translated message is thrown into
horizon.exceptions.handle, a UnicodeEncodeError is thrown in logging calls.

Also added in a test for this behavior.

Change-Id: I0bc71477d836daa0e27cdb10646b748fdc963f5d
Closes-Bug: 1284827
Merge "Accept translated exceptions in exceptions.handle"