engine,webadmin: Limit usage of Local ISO SD to Local DC

Using ISO Storage Domain which is local to one host in the multihost
environment can create issues because this SD is not visible by
other hosts, therefore there is a decision to limit its usage to
single host environment.

Change-Id: I4cfc3bb68581664fa6729e5cb8a163324e7fbc29
Bug-Url: https://bugzilla.redhat.com/993111
Signed-off-by: Sergey Gotliv <sgotliv@redhat.com>