abstract cache prefix creation
abstract cache prefix creation

Use canvas-builds to create prefix for cache images

refs DE-435
flag = none

[canvas-builds-refspec=d54d1f4dda757fbbb0372ad26defd8104d838e47]

Change-Id: Id1c6e29cb025f4a660bf891faa95df13f2978c33
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/255977
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Aaron Ogata <11ccf682c06d1508642f943a3962a1c3d00b8e44@instructure.com>
QA-Review: Andrea Cirulli <b4e55ef5ee4bae8ad31f7c81009bfc0af1714a1f@instructure.com>
Product-Review: Andrea Cirulli <b4e55ef5ee4bae8ad31f7c81009bfc0af1714a1f@instructure.com>

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