webadmin: Filter storage domains of different type in live storage migration

This change filters the destination domain by the type of the source domain
when performing live storage migration, if the source domain is a file
domain, the destination domains that will appear will be only file domains
and vice versa

Change-Id: I94f9feb9eb2b678e76653bed0b022ed05af40fc1
Signed-off-by: Tal Nisan <tnisan@redhat.com>