libvirt: rework membacking config to support future features
libvirt: rework membacking config to support future features

This commit reworks the method responsable to return
the guest configuration for the backend memory to make
it able to support other cases than hugepages

Change-Id: Ib32395d69ed3b8d0f6f1c0e7a3f6d31ed561d037

alaski/nova,BeyondTheClouds/nova,jianghuaw/nova,mikalstill/nova,cloudbase/nova,cernops/nova,apporc/nova,BeyondTheClouds/nova,mikalstill/nova,Juniper/nova,dims/nova,CEG-FYP-OpenStack/scheduler,hanlind/nova,mahak/nova,gooddata/openstack-nova,hanlind/nova,cyx1231st/nova,cloudbase/nova,alaski/nova,mikalstill/nova,gooddata/openstack-nova,klmitch/nova,devendermishrajio/nova,Juniper/nova,zhimin711/nova,vmturbo/nova,rajalokan/nova,openstack/nova,vmturbo/nova,klmitch/nova,mahak/nova,apporc/nova,jianghuaw/nova,klmitch/nova,hanlind/nova,cyx1231st/nova,Juniper/nova,cloudbase/nova,sebrandon1/nova,devendermishrajio/nova,zhimin711/nova,phenoxim/nova,rajalokan/nova,dims/nova,openstack/nova,cernops/nova,CEG-FYP-OpenStack/scheduler,mahak/nova,rahulunair/nova,jianghuaw/nova,vmturbo/nova,vmturbo/nova,sebrandon1/nova,jianghuaw/nova,rahulunair/nova,gooddata/openstack-nova,bigswitch/nova,NeCTAR-RC/nova,bigswitch/nova,openstack/nova,rahulunair/nova,klmitch/nova,Juniper/nova,rajalokan/nova,rajalokan/nova,sebrandon1/nova,BeyondTheClouds/nova,NeCTAR-RC/nova,cernops/nova,phenoxim/nova,gooddata/openstack-nova