improve reporting of build errors in the Ipc

JSON.stringify was not effective, but Error objects implement toString which should be informative.
I've tested by looking at what is logged now when FastClick is missing:
before (JSON.stringify): [pearson.brix.utils.Ipc] Error while building: {}
after (toString): [pearson.brix.utils.Ipc] Error while building: ReferenceError: FastClick is not defined
Fixed reference to food.
252: User context to System (PI ID, etc) for communication w/ GRID services

Jira: BRIX-252