include link to build in success message
include link to build in success message

refs DE-1159

[slack-reporting]

Change-Id: I24fb7707cc5757f6bff4142114a40d94cd4ca5b0
Reviewed-on: https://gerrit.instructure.com/c/dockerfiles/+/291484
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Andrea Cirulli <b4e55ef5ee4bae8ad31f7c81009bfc0af1714a1f@instructure.com>
QA-Review: Aaron Ogata <11ccf682c06d1508642f943a3962a1c3d00b8e44@instructure.com>

instructure/dockerfiles,instructure/dockerfiles,instructure/dockerfiles,instructure/dockerfiles