webadmin: rename import-vm related classes

The import-vm operation is about to be extended soon for different
use-cases. This patch rename the classes in the frontend which are
related to the import-vm operation such that it would reflect they are
related specifically to the import vm from export domain operation.

Change-Id: Ia36fae2b061ed51d76739546f9914abc06689d6e
Signed-off-by: Arik Hadas <ahadas@redhat.com>