NOJIRA Make Canvas proxy error logging more useful

Tracking the Canvas API bug yesterday was more difficult than it needed to be due to log messages void of request identifiers:

[2013-06-04 10:52:26] [WARN] [CalCentral] CanvasProxy connection failed: 404 {"status":"not_found","error_report_id":59064235,"message":"An error occurred."}

This pull request should give us enough to work with:

[2013-06-06 09:22:53] [WARN] [CalCentral] CanvasProxy connection failed for URL 'https://ucberkeley.test.instructure.com/api/v1/users/sis_user_id:211159/BADprofile', UID 211159: 404 {"status":"not_found","error_report_id":58846871,"message":"An error occurred."}