Capture exception for JSON load in virt.storage_users
Capture exception for JSON load in virt.storage_users

If CONF.instances_path/compute_nodes is empty when the storage_users
tries to register the storage use (virt.storage_users.register_storage_use)
the exception is uncaught and raised. As a consequence, the image cache
manager won't run.

Closes-Bug: #1252659

Change-Id: If9ed5e75b0bc0b8f3a7c5fd7ec88f6399e4e59c6

klmitch/nova,Metaswitch/calico-nova,orbitfp7/nova,saleemjaveds/https-github.com-openstack-nova,tealover/nova,barnsnake351/nova,iuliat/nova,badock/nova,alvarolopez/nova,double12gzh/nova,yosshy/nova,alaski/nova,zhimin711/nova,LoHChina/nova,cloudbase/nova-virtualbox,gooddata/openstack-nova,ruslanloman/nova,eharney/nova,luogangyi/bcec-nova,jianghuaw/nova,openstack/nova,BeyondTheClouds/nova,viggates/nova,yatinkumbhare/openstack-nova,thomasem/nova,Tehsmash/nova,virtualopensystems/nova,eonpatapon/nova,noironetworks/nova,CCI-MOC/nova,Tehsmash/nova,felixma/nova,rajalokan/nova,noironetworks/nova,badock/nova,projectcalico/calico-nova,takeshineshiro/nova,leilihh/nova,bigswitch/nova,Metaswitch/calico-nova,Juniper/nova,redhat-openstack/nova,gooddata/openstack-nova,ewindisch/nova,phenoxim/nova,NeCTAR-RC/nova,devendermishrajio/nova,berrange/nova,Francis-Liu/animated-broccoli,yosshy/nova,bgxavier/nova,eonpatapon/nova,mgagne/nova,Juniper/nova,affo/nova,projectcalico/calico-nova,rajalokan/nova,mahak/nova,edulramirez/nova,JioCloud/nova,vmturbo/nova,maelnor/nova,bgxavier/nova,tangfeixiong/nova,cloudbase/nova,jianghuaw/nova,affo/nova,alaski/nova,devoid/nova,rahulunair/nova,vmturbo/nova,shahar-stratoscale/nova,eharney/nova,JianyuWang/nova,TwinkleChawla/nova,CloudServer/nova,ted-gould/nova,varunarya10/nova_test_latest,cloudbase/nova-virtualbox,dawnpower/nova,watonyweng/nova,shail2810/nova,vladikr/nova_drafts,cernops/nova,klmitch/nova,rajalokan/nova,jianghuaw/nova,tudorvio/nova,shail2810/nova,hanlind/nova,alvarolopez/nova,redhat-openstack/nova,petrutlucian94/nova_dev,devoid/nova,zzicewind/nova,double12gzh/nova,blueboxgroup/nova,zaina/nova,apporc/nova,cyx1231st/nova,fnordahl/nova,cyx1231st/nova,mahak/nova,devendermishrajio/nova_test_latest,akash1808/nova,leilihh/novaha,zhimin711/nova,mmnelemane/nova,orbitfp7/nova,JioCloud/nova,sebrandon1/nova,JioCloud/nova_test_latest,petrutlucian94/nova,dims/nova,cernops/nova,jianghuaw/nova,petrutlucian94/nova,vmturbo/nova,angdraug/nova,sebrandon1/nova,zaina/nova,tangfeixiong/nova,leilihh/nova,cloudbase/nova,yatinkumbhare/openstack-nova,tianweizhang/nova,belmiromoreira/nova,openstack/nova,klmitch/nova,felixma/nova,eayunstack/nova,devendermishrajio/nova_test_latest,vmturbo/nova,watonyweng/nova,eayunstack/nova,mandeepdhami/nova,ruslanloman/nova,CCI-MOC/nova,bigswitch/nova,alexandrucoman/vbox-nova-driver,silenceli/nova,shahar-stratoscale/nova,rahulunair/nova,BeyondTheClouds/nova,whitepages/nova,angdraug/nova,zzicewind/nova,LoHChina/nova,mahak/nova,mandeepdhami/nova,virtualopensystems/nova,CEG-FYP-OpenStack/scheduler,MountainWei/nova,tanglei528/nova,tianweizhang/nova,whitepages/nova,TwinkleChawla/nova,tealover/nova,dawnpower/nova,ted-gould/nova,BeyondTheClouds/nova,akash1808/nova_test_latest,Stavitsky/nova,mikalstill/nova,cernops/nova,mikalstill/nova,mikalstill/nova,iuliat/nova,openstack/nova,mmnelemane/nova,blueboxgroup/nova,nikesh-mahalka/nova,joker946/nova,j-carpentier/nova,mgagne/nova,sebrandon1/nova,edulramirez/nova,fnordahl/nova,NeCTAR-RC/nova,tudorvio/nova,barnsnake351/nova,devendermishrajio/nova,JioCloud/nova_test_latest,viggates/nova,kimjaejoong/nova,scripnichenko/nova,Juniper/nova,akash1808/nova_test_latest,klmitch/nova,isyippee/nova,gooddata/openstack-nova,ewindisch/nova,CiscoSystems/nova,spring-week-topos/nova-week,belmiromoreira/nova,hanlind/nova,joker946/nova,akash1808/nova,jeffrey4l/nova,CloudServer/nova,phenoxim/nova,Yusuke1987/openstack_template,rahulunair/nova,thomasem/nova,jeffrey4l/nova,Stavitsky/nova,cloudbase/nova,Francis-Liu/animated-broccoli,leilihh/novaha,hanlind/nova,kimjaejoong/nova,adelina-t/nova,raildo/nova,rrader/nova-docker-plugin,silenceli/nova,tanglei528/nova,berrange/nova,nikesh-mahalka/nova,JianyuWang/nova,takeshineshiro/nova,scripnichenko/nova,adelina-t/nova,MountainWei/nova,j-carpentier/nova,raildo/nova,rrader/nova-docker-plugin,CEG-FYP-OpenStack/scheduler,vladikr/nova_drafts,dims/nova,saleemjaveds/https-github.com-openstack-nova,Yusuke1987/openstack_template,maelnor/nova,luogangyi/bcec-nova,apporc/nova,petrutlucian94/nova_dev,CiscoSystems/nova,spring-week-topos/nova-week,isyippee/nova,alexandrucoman/vbox-nova-driver,gooddata/openstack-nova,rajalokan/nova,varunarya10/nova_test_latest,Juniper/nova