Refactors kernel and ramdisk handling into their own method.
Refactors kernel and ramdisk handling into their own method.

The size of `_create_instance` is making it increasingly difficult to
work with. This is part of a series of patches aims to break it up into
smaller, more digestible pieces.

Change-Id: Ic668f0414937b255b1b1e1392c204307665822aa

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