Add JSON-Schema note to api_plugins.rst
Add JSON-Schema note to api_plugins.rst

Nova v2.1 API validates a request with JSON-Schema, and there are
some specific usage on that. This patch adds it to the rst file
for the implementation hint.

Change-Id: I4edac8b6b53d198f2a237bb163b8975528319c9b

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