allow docker_dev_setup to work without upstart or dory
allow docker_dev_setup to work without upstart or dory

Allow systems without service command, or users that don't want to
install dory, to be able to still run docker_dev_setup.sh. Request
from MasteryConnect.
Systems without service command default to systemctl
Allowed to opt out of dory

flag = none

Test Plan:
- Jenkins Passes
- No changes for current users
- On a system wihtout service command, script still is able to
  start docker with systemctl
- Without dory installed, prompted to skip dory
  - if skipped setup continues and successfully installs canvas
  - if not skipped, script exits so user can install dory
    - rerunning the script after install is successful

Change-Id: I420a020fc27f1c12168ef0edfa55b537fb7a8010
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/257787
Reviewed-by: Aaron Ogata <11ccf682c06d1508642f943a3962a1c3d00b8e44@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: James Butters <4c5a489c9bb72d41f20b3b22aaf4c9b864e32f20@instructure.com>
Product-Review: James Butters <4c5a489c9bb72d41f20b3b22aaf4c9b864e32f20@instructure.com>

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