api: raise ClientSideError rather than ValueError
api: raise ClientSideError rather than ValueError

This also enables the error message to be translatable.

Change-Id: If63ba0f7bc04eb490578c7598875407e796700aa

fabian4/ceilometer,sileht/aodh,NeCTAR-RC/ceilometer,NeCTAR-RC/ceilometer,maestro-hybrid-cloud/ceilometer,Juniper/ceilometer,luogangyi/Ceilometer-oVirt,m1093782566/openstack_org_ceilometer,luogangyi/Ceilometer-oVirt,openstack/ceilometer,chungg/aodh,cernops/ceilometer,cernops/ceilometer,mathslinux/ceilometer,pkilambi/ceilometer,pczerkas/aodh,openstack/aodh,Juniper/ceilometer,MisterPup/Ceilometer-Juno-Extension,froyobin/ceilometer,openstack/aodh,pczerkas/aodh,r-mibu/ceilometer,fabian4/ceilometer,idegtiarov/ceilometer,idegtiarov/ceilometer,openstack/ceilometer,isyippee/ceilometer,r-mibu/ceilometer,redhat-openstack/ceilometer,pkilambi/ceilometer,chungg/aodh,m1093782566/openstack_org_ceilometer,tanglei528/ceilometer,eayunstack/ceilometer,mathslinux/ceilometer,tanglei528/ceilometer,isyippee/ceilometer,maestro-hybrid-cloud/ceilometer,froyobin/ceilometer,ityaptin/ceilometer,MisterPup/Ceilometer-Juno-Extension,NeCTAR-RC/ceilometer,sileht/aodh,tanglei528/ceilometer,redhat-openstack/ceilometer,ityaptin/ceilometer,eayunstack/ceilometer