libvirt: update docstring in blockinfo module for disk_info
libvirt: update docstring in blockinfo module for disk_info

The docstring was listing disk_info as a tuple but it's a dict in the
code and it wasn't pointing out that boot_index is an optional field.

Long-term we should probably convert disk_info into an object (doesn't
need to be versioned, but would be cleaner as an object). I started
doing this with a namedtuple but the format and boot_index fields being
optional makes namedtuple a bit messy.

Change-Id: I6721cad9245e8722481c4c63023bb8b7193317ac

klmitch/nova,CCI-MOC/nova,barnsnake351/nova,whitepages/nova,watonyweng/nova,LoHChina/nova,rajalokan/nova,gooddata/openstack-nova,mikalstill/nova,BeyondTheClouds/nova,cernops/nova,vmturbo/nova,JioCloud/nova_test_latest,vmturbo/nova,iuliat/nova,dims/nova,TwinkleChawla/nova,rajalokan/nova,yosshy/nova,klmitch/nova,mmnelemane/nova,gooddata/openstack-nova,alaski/nova,zhimin711/nova,Juniper/nova,varunarya10/nova_test_latest,cloudbase/nova,rahulunair/nova,felixma/nova,scripnichenko/nova,gooddata/openstack-nova,Juniper/nova,raildo/nova,JioCloud/nova_test_latest,felixma/nova,whitepages/nova,j-carpentier/nova,BeyondTheClouds/nova,JianyuWang/nova,openstack/nova,jianghuaw/nova,CEG-FYP-OpenStack/scheduler,raildo/nova,hanlind/nova,cernops/nova,phenoxim/nova,mahak/nova,sebrandon1/nova,isyippee/nova,devendermishrajio/nova_test_latest,jianghuaw/nova,ted-gould/nova,klmitch/nova,ted-gould/nova,Juniper/nova,devendermishrajio/nova_test_latest,dims/nova,barnsnake351/nova,takeshineshiro/nova,shail2810/nova,yosshy/nova,rahulunair/nova,shail2810/nova,isyippee/nova,klmitch/nova,Francis-Liu/animated-broccoli,watonyweng/nova,takeshineshiro/nova,ruslanloman/nova,cyx1231st/nova,cernops/nova,LoHChina/nova,MountainWei/nova,jianghuaw/nova,fnordahl/nova,edulramirez/nova,jianghuaw/nova,akash1808/nova_test_latest,sebrandon1/nova,noironetworks/nova,zzicewind/nova,rajalokan/nova,devendermishrajio/nova,openstack/nova,phenoxim/nova,rahulunair/nova,iuliat/nova,gooddata/openstack-nova,openstack/nova,hanlind/nova,zzicewind/nova,mmnelemane/nova,JianyuWang/nova,cloudbase/nova,CCI-MOC/nova,fnordahl/nova,Francis-Liu/animated-broccoli,NeCTAR-RC/nova,bigswitch/nova,j-carpentier/nova,mahak/nova,edulramirez/nova,akash1808/nova_test_latest,cyx1231st/nova,mahak/nova,varunarya10/nova_test_latest,bigswitch/nova,rajalokan/nova,cloudbase/nova,scripnichenko/nova,zhimin711/nova,nikesh-mahalka/nova,noironetworks/nova,mikalstill/nova,NeCTAR-RC/nova,ruslanloman/nova,alaski/nova,TwinkleChawla/nova,vmturbo/nova,sebrandon1/nova,BeyondTheClouds/nova,CEG-FYP-OpenStack/scheduler,apporc/nova,devendermishrajio/nova,mikalstill/nova,apporc/nova,MountainWei/nova,nikesh-mahalka/nova,hanlind/nova,Juniper/nova,vmturbo/nova