filter out localhost and local ips from canvashttp

test plan:
* use the API to queue a content migration for a course
 with a parameter 'file_url' set to a local url
 (i.e. 'localhost:3000/500.html')
* it should not download the file and allow the file
 to be downloaded on the content migrations page
 for the course

* create a link to a local file
 in a piece of course content (i.e. a page)
* run the course link validator
* it should not actually check if the link exists locally
 or not, but rather always flag the link

closes #SEC-606 SEC-607

Change-Id: I671c017ec93d88446df77d716725fff8874622bc
Reviewed-on: https://gerrit.instructure.com/125118


Tested-by: Jenkins
Reviewed-by: Brad Horrocks <bhorrocks@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Heath Hales <hhales@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>