Add image_size_cap documentation
Add image_size_cap documentation

Add documentation for the 'image_size_cap' parameter.

Addresses bug 1158723.

Change-Id: If6d28a3837dc875b7c8e3e18dd5058eb07b40638

vuntz/glance,wkoathp/glance,citrix-openstack-build/glance,cloudbau/glance,darren-wang/gl,redhat-openstack/glance,scripnichenko/glance,citrix-openstack-build/glance,sigmavirus24/glance,klmitch/glance,jumpstarter-io/glance,ozamiatin/glance,scripnichenko/glance,saeki-masaki/glance,rickerc/glance_audit,akash1808/glance,dims/glance,darren-wang/gl,stevelle/glance,ntt-sic/glance,redhat-openstack/glance,saeki-masaki/glance,SUSE-Cloud/glance,cloudbau/glance,rajalokan/glance,vuntz/glance,rajalokan/glance,jumpstarter-io/glance,openstack/glance,takeshineshiro/glance,JioCloud/glance,akash1808/glance,SUSE-Cloud/glance,kfwang/Glance-OVA-OVF,openstack/glance,tanglei528/glance,kfwang/Glance-OVA-OVF,JioCloud/glance,wkoathp/glance,klmitch/glance,rickerc/glance_audit,dims/glance,takeshineshiro/glance,ntt-sic/glance,ozamiatin/glance,paramite/glance,stevelle/glance,sigmavirus24/glance,paramite/glance,tanglei528/glance,openstack/glance