webadmin: setting destination cluster when importing glance templates

When importing glance templates it is useful to allow selecting a
cluster for this template.
This patch adds this functionality

Change-Id: I828590dae0b68b9bb3da9fc136084c9673cd4c8d
Bug-Url: https://bugzilla.redhat.com/1070394
Signed-off-by: Oved Ourfali <oourfali@redhat.com>