engine: initialize scheduling manager from InitBackendServicesOnStartupBean

Schedling manager initialize made public, call removed from constructor
and added to InitBackendServicesOnStartupBean. Additional logging for
better tracing.

Change-Id: Ic74d28c2aa9700527f6217f4de2a2b4527286317
Signed-off-by: Laszlo Hornyak <lhornyak@redhat.com>
engine: start discovery thread only if enabled

Checks the external scheduler configuration before starting the external
scheduler discovery thread. Added logging for better tracing.

Change-Id: Ibac067131d3725d39afaf2f4941165eccdb60372
Signed-off-by: Laszlo Hornyak <lhornyak@redhat.com>
engine: handle unavailable external scheduler

handle the case when the external scheduler is not available when
calculating scores for the hosts

Change-Id: Ib5e60b4be166da95c1d46449b222e14220963784
Signed-off-by: Laszlo Hornyak <lhornyak@redhat.com>