core: mark GetVirtioScsiControllers as user query

Marking GetVirtioScsiControllers query as VdcQueryAuthType.User
since it's being used by the user portal.

Change-Id: I268b39bc85525a270998c10b67c2463a45a08a26
Bug-Url: https://bugzilla.redhat.com/1016826
Signed-off-by: Daniel Erez <derez@redhat.com>