Support dynamic loading of provided implementations of PORTAL SDK's
`org.onap.portalsdk.core.auth.LoginStrategy` interface.
VID will load the class defined by `login.strategy.classname`
configuration parameter. Default will keep current ONAP's dev login.
Change-Id: I956a1f3376455211398769f3193703129b779871
Issue-ID: VID-594
Signed-off-by: Ittay Stern <ittay.stern@att.com>