core: set current user in import glance image as template

Importing a glance image may take a while.
Thus, when calling AddVmTemplate the session may no longer be valid, so getCurrentUser() will return null.
This patch sets the user in the parameters class. CommandBase makes sure to take that in case getCurrentUser() is null

Change-Id: I69dd535db983471ba31b8d427b4e0a373f1f7dc4
Bug-Url: https://bugzilla.redhat.com/1085712
Signed-off-by: Oved Ourfali <oourfali@redhat.com>