Store "null api version" as 0.0
Store "null api version" as 0.0

Nova API doesn't have 0 version, so we can use 0.0 for Null APIVersion.
It will help to write simple comparison methods.

Change-Id: I9010007e6e5a92a378299ccb0d674b30fdabc365

Juniper/nova,mmnelemane/nova,alaski/nova,zhimin711/nova,devendermishrajio/nova,NeCTAR-RC/nova,scripnichenko/nova,rajalokan/nova,ted-gould/nova,edulramirez/nova,j-carpentier/nova,ted-gould/nova,gooddata/openstack-nova,cyx1231st/nova,cloudbase/nova,Juniper/nova,bigswitch/nova,rajalokan/nova,fnordahl/nova,vmturbo/nova,openstack/nova,Francis-Liu/animated-broccoli,klmitch/nova,barnsnake351/nova,mahak/nova,nikesh-mahalka/nova,felixma/nova,rahulunair/nova,fnordahl/nova,j-carpentier/nova,edulramirez/nova,vmturbo/nova,JianyuWang/nova,rajalokan/nova,CEG-FYP-OpenStack/scheduler,mahak/nova,vmturbo/nova,whitepages/nova,noironetworks/nova,dims/nova,barnsnake351/nova,gooddata/openstack-nova,BeyondTheClouds/nova,BeyondTheClouds/nova,zhimin711/nova,cloudbase/nova,alaski/nova,apporc/nova,klmitch/nova,sebrandon1/nova,jianghuaw/nova,hanlind/nova,hanlind/nova,TwinkleChawla/nova,nikesh-mahalka/nova,hanlind/nova,shail2810/nova,dims/nova,bigswitch/nova,MountainWei/nova,mikalstill/nova,Francis-Liu/animated-broccoli,mikalstill/nova,CCI-MOC/nova,Juniper/nova,CCI-MOC/nova,noironetworks/nova,jianghuaw/nova,CEG-FYP-OpenStack/scheduler,devendermishrajio/nova,whitepages/nova,yosshy/nova,TwinkleChawla/nova,gooddata/openstack-nova,JianyuWang/nova,cernops/nova,cyx1231st/nova,raildo/nova,BeyondTheClouds/nova,yosshy/nova,openstack/nova,mahak/nova,MountainWei/nova,scripnichenko/nova,rajalokan/nova,NeCTAR-RC/nova,cloudbase/nova,gooddata/openstack-nova,vmturbo/nova,jianghuaw/nova,mmnelemane/nova,cernops/nova,phenoxim/nova,klmitch/nova,mikalstill/nova,rahulunair/nova,apporc/nova,openstack/nova,shail2810/nova,sebrandon1/nova,cernops/nova,sebrandon1/nova,rahulunair/nova,raildo/nova,isyippee/nova,jianghuaw/nova,klmitch/nova,Juniper/nova,isyippee/nova,felixma/nova,phenoxim/nova