Add slack output to fsc
Add slack output to fsc

Test-plan:
 - look at previous PS and their corresponding FSC jobs
   and verify the jobs pass/fail accordingly
 - go to #flakey_spec_catcher_noisy and click the links
   verify that the correspond to the right builds
   and that the slack message colors correspond correctly
   to pass / fail

Change-Id: I00678ea186196f4202f6f3aa3620e67869bef26c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/229240
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Rex Fleischer <360d56e185853f069087eaa5288d1374fc56d750@instructure.com>
QA-Review: Brian Watson <4411c2aac809443ec63e2dd517de0f2dbc7408c6@instructure.com>
Product-Review: Brian Watson <4411c2aac809443ec63e2dd517de0f2dbc7408c6@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms