Cleanup _convert_block_devices
Cleanup _convert_block_devices

_convert_block_devices was instantiating 2 objects for every 1
returned due to the _is_transformable test. This change simplifies the
code by removing the nested function, and at the same time does the
conversion in a single pass, which is more efficient.

Change-Id: Id6b583a1c08d684fcff073dd0289be8e3919ba0a

tudorvio/nova,adelina-t/nova,scripnichenko/nova,shail2810/nova,thomasem/nova,gooddata/openstack-nova,raildo/nova,rahulunair/nova,blueboxgroup/nova,whitepages/nova,zzicewind/nova,Tehsmash/nova,shail2810/nova,rahulunair/nova,whitepages/nova,projectcalico/calico-nova,maelnor/nova,JioCloud/nova,yosshy/nova,belmiromoreira/nova,blueboxgroup/nova,mikalstill/nova,devendermishrajio/nova,Juniper/nova,belmiromoreira/nova,rajalokan/nova,akash1808/nova,devendermishrajio/nova_test_latest,cyx1231st/nova,Metaswitch/calico-nova,mikalstill/nova,rajalokan/nova,double12gzh/nova,takeshineshiro/nova,affo/nova,mmnelemane/nova,zaina/nova,CloudServer/nova,bgxavier/nova,jeffrey4l/nova,tangfeixiong/nova,apporc/nova,alvarolopez/nova,ruslanloman/nova,klmitch/nova,bigswitch/nova,j-carpentier/nova,akash1808/nova_test_latest,MountainWei/nova,joker946/nova,openstack/nova,NeCTAR-RC/nova,mgagne/nova,cloudbase/nova,ted-gould/nova,hanlind/nova,tudorvio/nova,apporc/nova,j-carpentier/nova,alaski/nova,Juniper/nova,affo/nova,scripnichenko/nova,mahak/nova,varunarya10/nova_test_latest,gooddata/openstack-nova,TwinkleChawla/nova,watonyweng/nova,yatinkumbhare/openstack-nova,Stavitsky/nova,cernops/nova,fnordahl/nova,mandeepdhami/nova,iuliat/nova,ted-gould/nova,BeyondTheClouds/nova,cloudbase/nova,eonpatapon/nova,raildo/nova,jianghuaw/nova,Juniper/nova,BeyondTheClouds/nova,yosshy/nova,cloudbase/nova-virtualbox,berrange/nova,Yusuke1987/openstack_template,sebrandon1/nova,felixma/nova,adelina-t/nova,kimjaejoong/nova,rahulunair/nova,petrutlucian94/nova,devendermishrajio/nova,mahak/nova,phenoxim/nova,Tehsmash/nova,CEG-FYP-OpenStack/scheduler,jianghuaw/nova,alexandrucoman/vbox-nova-driver,akash1808/nova_test_latest,cloudbase/nova-virtualbox,isyippee/nova,Yusuke1987/openstack_template,dawnpower/nova,edulramirez/nova,cernops/nova,BeyondTheClouds/nova,jianghuaw/nova,tangfeixiong/nova,double12gzh/nova,barnsnake351/nova,takeshineshiro/nova,dims/nova,Francis-Liu/animated-broccoli,nikesh-mahalka/nova,CCI-MOC/nova,mgagne/nova,iuliat/nova,sebrandon1/nova,alaski/nova,kimjaejoong/nova,barnsnake351/nova,alexandrucoman/vbox-nova-driver,watonyweng/nova,vmturbo/nova,bgxavier/nova,openstack/nova,joker946/nova,silenceli/nova,bigswitch/nova,JioCloud/nova,zhimin711/nova,mikalstill/nova,badock/nova,eonpatapon/nova,LoHChina/nova,cernops/nova,angdraug/nova,gooddata/openstack-nova,fnordahl/nova,sebrandon1/nova,tealover/nova,projectcalico/calico-nova,alvarolopez/nova,cyx1231st/nova,vmturbo/nova,hanlind/nova,angdraug/nova,zhimin711/nova,cloudbase/nova,yatinkumbhare/openstack-nova,petrutlucian94/nova,dims/nova,berrange/nova,felixma/nova,JianyuWang/nova,orbitfp7/nova,CCI-MOC/nova,tealover/nova,jianghuaw/nova,CEG-FYP-OpenStack/scheduler,openstack/nova,Metaswitch/calico-nova,rajalokan/nova,NeCTAR-RC/nova,orbitfp7/nova,hanlind/nova,zaina/nova,mandeepdhami/nova,thomasem/nova,nikesh-mahalka/nova,silenceli/nova,noironetworks/nova,edulramirez/nova,rajalokan/nova,jeffrey4l/nova,klmitch/nova,isyippee/nova,devendermishrajio/nova_test_latest,dawnpower/nova,gooddata/openstack-nova,noironetworks/nova,klmitch/nova,akash1808/nova,mahak/nova,JianyuWang/nova,vmturbo/nova,vmturbo/nova,LoHChina/nova,maelnor/nova,Juniper/nova,badock/nova,Francis-Liu/animated-broccoli,Stavitsky/nova,klmitch/nova,CloudServer/nova,phenoxim/nova,ruslanloman/nova,JioCloud/nova_test_latest,MountainWei/nova,zzicewind/nova,mmnelemane/nova,TwinkleChawla/nova,JioCloud/nova_test_latest,varunarya10/nova_test_latest