make the docker clean more concise
make the docker clean more concise

fixes: CCI-249
flag = none

Test-Plan:
read though the logs for the clean script and ensure
that it is removing all the stuff except for db and master canvas.

Change-Id: I282a072d95ef19b32be98faee2992ae14a7d9c9d
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/227748
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: Rex Fleischer <360d56e185853f069087eaa5288d1374fc56d750@instructure.com>
Product-Review: Rex Fleischer <360d56e185853f069087eaa5288d1374fc56d750@instructure.com>
Reviewed-by: James Butters <4c5a489c9bb72d41f20b3b22aaf4c9b864e32f20@instructure.com>
Reviewed-by: Derek Bender <d24d8a7ee520e34b1cec38800225d9f36b552df7@instructure.com>

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