don't change anchor references to relative urls on import

Test Plan:
 * import a common cartridge package with html that has a
   <a href="#something">hey</a> in it
 * That href value should not change after imported

refs PLAT-433

Change-Id: I84229c5f587020ebc4279baf9bb7138db8c79223
Reviewed-on: https://gerrit.instructure.com/32152
Reviewed-by: Nathan Mills <nathanm@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>