Simplify file hashing
Simplify file hashing

Since map() is not lazy, hash_file() created huge lists filled with
`None` when hashing large files. Rewriting it to a simple loop prevents
that.

Change-Id: I65681f905bacc2afda52853bbe9e364b89f515a8

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