temporary fix for screenreader support on blueprint's flash messages
temporary fix for screenreader support on blueprint's flash messages

this is a temporary fix until instui's next release. Then we should
merge g/114346/ to replace this change

fixes MC-171

test plan:
  - create a blueprint course
  - make some changes so there are unsynced changes
  - open the blueprint sidebar, the sync button should be displayed
  - disconnect from the network or kill rails server
  - at this point, be sure you have a screenreader rnning
  - click Sync
  > expect an alert saying there was an error. The screenreader should
  > announce it too

Change-Id: I5e84c63f0df7ec576d00b05134cbda022d6a158e
Reviewed-on: https://gerrit.instructure.com/114612
Tested-by: Jenkins
Reviewed-by: Felix Milea-Ciobanu <9384aa226ac9d3237ed0bc52e18ffcb251ee0bf7@instructure.com>
QA-Review: David Tan <6283e310a2278fc51bdc4fb5974f70dd9c3366b9@instructure.com>
Product-Review: Nathan Rogowski <2e8aa918660411855c6d44d5bb2da677aa033255@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,venturehive/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms