Don't strip the verifier from user-context files

fixes #CNVS-11032

If you were to use a files link that didnt start
with "/files" (like "/users/x/files/y" or a link
with a full host name), it would
still strip the verifier out, which would make the
file not appear to other users.  This fixes
the problem.

TEST PLAN:
 -login as a user
 -go to files and upload an image to *your* folder
    (rather than the folder for a course or something)
 -obtain a link to that file with it's verifier param through
    whatever means you prefer (simplest is to get the download
    link and then use the console to get the UUID from that
    Attachment record and use that as "verifer=[blah]" at
    the end of the url for the file)
 -post a discussion reply using that link to embed an image
    in the reply.
 -login as a different user and look at the discussionr reply;
  you should be able to see the image in the discussion reply.

Change-Id: I2e9123f08cda0e6949e8f9a8d12ba50b98de49e0
Reviewed-on: https://gerrit.instructure.com/40430
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Hilary Scharton <hilary@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>