Add a note about the 400 response not requiring a microversion
Add a note about the 400 response not requiring a microversion

As the API validation code always return 400 when request with
invalid json body, so 400 is an available status code for all the
Nova API. Then no microversion bump required for fixing 500 to 400.

Change-Id: I0454e95cd0655c910fad8b39ead2b5edab216b68
Related-Bug: 1471239

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