rpc: reduce sleep time
rpc: reduce sleep time

And add a comment on what it's used for

Change-Id: I6225346979299379e8d566081a2586c7c4525e20

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