Add version constraint for coverage
Add version constraint for coverage

Python coverage lower than 3.6 causes issues when running the whole
test suite. Some arguments are randomly mixed up with script names,
resulting in unittest failures like this:

UnexpectedMethodCallError: Unexpected method call.  unexpected:-  expected:+
- exists.__call__('/tmp/buildd/.../nova/virt/images.py') -> None
+ exists.__call__('/some/path') -> True

Change-Id: Iadb6d046e3acc75c6ed5abffcfc1abda82aeee4f

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