Rollbar interceptor error handling

[skaestle]

we have an issue on the ratings app where the rollbar notification results in an Encoding::UndefinedConversionError (https://rollbar.com/local.ch/ratings/items/10/)

we assume this masks the underlying cause of the initial rollbar warning.

this is an attempt of recovering in such a case, by sanitizing the data sent to rollbar.

Att:

• the rspecs are a bit awkward. I did my best to make them concise
• if someone knows a better way of setting up a spy that first throws an exception and the second time not, im all ears!