don't explode if a 413 didn't set Retry-After
don't explode if a 413 didn't set Retry-After

We use 413 error code not only for temporary out of memory
conditions but also for over quota issues. These kinds of
requests don't set a Retry-After header, but the code assumed
that was a valid key, thus exploding on a KeyError. Issue
caught in looking at tempest traces.

Fixes bug #1079387

Change-Id: Id406ab0799a35220b189b2e5292be092eb821ec5

j-carpentier/nova,CCI-MOC/nova,Triv90/Nova,takeshineshiro/nova,zaina/nova,klmitch/nova,edulramirez/nova,aristanetworks/arista-ovs-nova,Triv90/Nova,ted-gould/nova,fajoy/nova,dawnpower/nova,yosshy/nova,adelina-t/nova,akash1808/nova_test_latest,jianghuaw/nova,vladikr/nova_drafts,Triv90/Nova,openstack/nova,klmitch/nova,iuliat/nova,mikalstill/nova,petrutlucian94/nova_dev,akash1808/nova_test_latest,maelnor/nova,Yuriy-Leonov/nova,barnsnake351/nova,maoy/zknova,tealover/nova,sridevikoushik31/openstack,yosshy/nova,iuliat/nova,tealover/nova,thomasem/nova,saleemjaveds/https-github.com-openstack-nova,yatinkumbhare/openstack-nova,projectcalico/calico-nova,rickerc/nova_audit,affo/nova,gspilio/nova,imsplitbit/nova,bclau/nova,NeCTAR-RC/nova,leilihh/nova,hanlind/nova,double12gzh/nova,badock/nova,gooddata/openstack-nova,raildo/nova,tianweizhang/nova,TwinkleChawla/nova,nikesh-mahalka/nova,imsplitbit/nova,leilihh/novaha,CiscoSystems/nova,tudorvio/nova,jianghuaw/nova,Brocade-OpenSource/OpenStack-DNRM-Nova,belmiromoreira/nova,cloudbase/nova,houshengbo/nova_vmware_compute_driver,double12gzh/nova,Yusuke1987/openstack_template,aristanetworks/arista-ovs-nova,alexandrucoman/vbox-nova-driver,watonyweng/nova,alvarolopez/nova,affo/nova,devendermishrajio/nova_test_latest,JianyuWang/nova,orbitfp7/nova,MountainWei/nova,luogangyi/bcec-nova,tianweizhang/nova,klmitch/nova,dstroppa/openstack-smartos-nova-grizzly,mmnelemane/nova,maheshp/novatest,cloudbase/nova-virtualbox,JioCloud/nova,devendermishrajio/nova_test_latest,bgxavier/nova,isyippee/nova,shahar-stratoscale/nova,viggates/nova,hanlind/nova,mgagne/nova,BeyondTheClouds/nova,sridevikoushik31/openstack,maheshp/novatest,rajalokan/nova,mikalstill/nova,cloudbau/nova,silenceli/nova,yrobla/nova,gooddata/openstack-nova,bclau/nova,silenceli/nova,houshengbo/nova_vmware_compute_driver,jeffrey4l/nova,saleemjaveds/https-github.com-openstack-nova,zaina/nova,vmturbo/nova,alaski/nova,adelina-t/nova,cernops/nova,maoy/zknova,Tehsmash/nova,virtualopensystems/nova,apporc/nova,dawnpower/nova,belmiromoreira/nova,sridevikoushik31/nova,fnordahl/nova,rrader/nova-docker-plugin,yrobla/nova,dstroppa/openstack-smartos-nova-grizzly,bgxavier/nova,Stavitsky/nova,cernops/nova,CloudServer/nova,gspilio/nova,sacharya/nova,ntt-sic/nova,tudorvio/nova,houshengbo/nova_vmware_compute_driver,eonpatapon/nova,angdraug/nova,noironetworks/nova,mgagne/nova,angdraug/nova,gspilio/nova,SUSE-Cloud/nova,vmturbo/nova,petrutlucian94/nova_dev,joker946/nova,LoHChina/nova,akash1808/nova,MountainWei/nova,citrix-openstack-build/nova,kimjaejoong/nova,tanglei528/nova,shootstar/novatest,fajoy/nova,sridevikoushik31/nova,tanglei528/nova,mahak/nova,luogangyi/bcec-nova,barnsnake351/nova,Francis-Liu/animated-broccoli,whitepages/nova,maelnor/nova,ntt-sic/nova,varunarya10/nova_test_latest,tangfeixiong/nova,viggates/nova,CiscoSystems/nova,whitepages/nova,cloudbase/nova,leilihh/novaha,SUSE-Cloud/nova,Metaswitch/calico-nova,zzicewind/nova,alexandrucoman/vbox-nova-driver,hanlind/nova,yatinkumbhare/openstack-nova,sridevikoushik31/openstack,cloudbase/nova,scripnichenko/nova,ewindisch/nova,mikalstill/nova,phenoxim/nova,varunarya10/nova_test_latest,dims/nova,jianghuaw/nova,BeyondTheClouds/nova,bigswitch/nova,mandeepdhami/nova,blueboxgroup/nova,mahak/nova,Juniper/nova,qwefi/nova,CCI-MOC/nova,Juniper/nova,eayunstack/nova,Yuriy-Leonov/nova,TieWei/nova,DirectXMan12/nova-hacking,OpenAcademy-OpenStack/nova-scheduler,BeyondTheClouds/nova,bigswitch/nova,vmturbo/nova,JianyuWang/nova,spring-week-topos/nova-week,citrix-openstack-build/nova,eharney/nova,Metaswitch/calico-nova,kimjaejoong/nova,gooddata/openstack-nova,yrobla/nova,devoid/nova,ted-gould/nova,mmnelemane/nova,devoid/nova,LoHChina/nova,devendermishrajio/nova,rahulunair/nova,rajalokan/nova,badock/nova,tangfeixiong/nova,petrutlucian94/nova,rajalokan/nova,cyx1231st/nova,OpenAcademy-OpenStack/nova-scheduler,shootstar/novatest,aristanetworks/arista-ovs-nova,fajoy/nova,mahak/nova,ruslanloman/nova,dstroppa/openstack-smartos-nova-grizzly,eharney/nova,DirectXMan12/nova-hacking,sacharya/nova,shahar-stratoscale/nova,maoy/zknova,shail2810/nova,rahulunair/nova,alaski/nova,ewindisch/nova,shail2810/nova,noironetworks/nova,TieWei/nova,Stavitsky/nova,plumgrid/plumgrid-nova,watonyweng/nova,rahulunair/nova,vmturbo/nova,virtualopensystems/nova,orbitfp7/nova,raildo/nova,cloudbau/nova,sridevikoushik31/nova,akash1808/nova,fnordahl/nova,Tehsmash/nova,vladikr/nova_drafts,TwinkleChawla/nova,ruslanloman/nova,devendermishrajio/nova,zzicewind/nova,thomasem/nova,phenoxim/nova,eonpatapon/nova,openstack/nova,CloudServer/nova,Brocade-OpenSource/OpenStack-DNRM-Nova,JioCloud/nova_test_latest,nikesh-mahalka/nova,rrader/nova-docker-plugin,CEG-FYP-OpenStack/scheduler,zhimin711/nova,dims/nova,redhat-openstack/nova,jeffrey4l/nova,takeshineshiro/nova,joker946/nova,JioCloud/nova,apporc/nova,JioCloud/nova_test_latest,plumgrid/plumgrid-nova,cloudbase/nova-virtualbox,eayunstack/nova,sebrandon1/nova,Juniper/nova,blueboxgroup/nova,sebrandon1/nova,alvarolopez/nova,leilihh/nova,maheshp/novatest,sridevikoushik31/nova,klmitch/nova,redhat-openstack/nova,openstack/nova,isyippee/nova,felixma/nova,Juniper/nova,berrange/nova,zhimin711/nova,CEG-FYP-OpenStack/scheduler,cyx1231st/nova,DirectXMan12/nova-hacking,jianghuaw/nova,j-carpentier/nova,sebrandon1/nova,berrange/nova,gooddata/openstack-nova,projectcalico/calico-nova,rajalokan/nova,Yusuke1987/openstack_template,rickerc/nova_audit,mandeepdhami/nova,scripnichenko/nova,Francis-Liu/animated-broccoli,edulramirez/nova,felixma/nova,cernops/nova,spring-week-topos/nova-week,petrutlucian94/nova,NeCTAR-RC/nova,qwefi/nova