[CT-1267] Convert non-structured messages generated in exceptions.py to structured events

[gshank]

We have a number of logging events in which the string message is generated by external utilities, mostly in various functions in exceptions.py. Because of this, the actual information used to structure the message is not included in the logging event. These events can be identified by the fact that they contain a "msg" field instead of various structured fields.

Refactor these messages so that more of the formatting code is moved into the logging event code, and so that the events capture the strings used to construct the message.