packaging: engine-upgrade - Don't list duplicate packages
packaging: engine-upgrade - Don't list duplicate packages

The updateAvailable method used to list all available packages
instead of just updates, which might have caused duplicate entries in
the candidates-for-update list.

Change-Id: I4af8abb6337d269f707559c8139ee62b9af1f1cb
Signed-off-by: Ofer Schreiber <3681fb3205baf680cd6a957dddfb09244e62ce7a@redhat.com>

halober/ovirt-engine,walteryang47/ovirt-engine,yapengsong/ovirt-engine,eayun/ovirt-engine,derekhiggins/ovirt-engine,walteryang47/ovirt-engine,walteryang47/ovirt-engine,halober/ovirt-engine,yapengsong/ovirt-engine,OpenUniversity/ovirt-engine,zerodengxinchao/ovirt-engine,yapengsong/ovirt-engine,zerodengxinchao/ovirt-engine,derekhiggins/ovirt-engine,halober/ovirt-engine,halober/ovirt-engine,yingyun001/ovirt-engine,yapengsong/ovirt-engine,yingyun001/ovirt-engine,yapengsong/ovirt-engine,zerodengxinchao/ovirt-engine,eayun/ovirt-engine,derekhiggins/ovirt-engine,zerodengxinchao/ovirt-engine,yingyun001/ovirt-engine,OpenUniversity/ovirt-engine,yingyun001/ovirt-engine,walteryang47/ovirt-engine,eayun/ovirt-engine,zerodengxinchao/ovirt-engine,OpenUniversity/ovirt-engine,OpenUniversity/ovirt-engine,OpenUniversity/ovirt-engine,eayun/ovirt-engine,yingyun001/ovirt-engine,derekhiggins/ovirt-engine,eayun/ovirt-engine,walteryang47/ovirt-engine