azure: Run Base and XMLRPC tests is isolated network
    
    The tests in these envs make DNS requests to wild(internet) NSs,
    though usually tests assume the opposite making requests to
    `test.` zone. This makes CI unstable and dependent on wild
    resolvers and logically wrong.
    
    In future there can be tests which may want to check BIND as
    resolver(cache) for external networks. In this case such tests
    should be placed on not isolated mode.
    
    By default, a test env is not isolated from internet(as it was
    before), but it may be a good idea to change this default in
    future.
    
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>