HyperV: do not log twice with different level.
HyperV: do not log twice with different level.

It is not necessary to log remove_vm_snapshot error with both
LOG.exception and LOG.warning

Change-Id: Iee503498119a181de9b35f5e32ca45a596dbb20a

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