Replace binding:capabilities with binding:vif_details

Replace binding:capabilities with binding:vif_details

In addition to binding:vif_type, the neutron core plugin needs to
supply various information to nova's VIF driver, such as VIF security
details and PCI details when SR-IOV is being used. This information is
read-only, requires admin privileges, and is not intended for normal
users. Rather than add separate mechanisms throughout the stack for
each such requirement, the binding:capabilities port attibute, which
is a dictionary and is not currently not used by nova, is renamed to
binding:vif_details to serve as a general-purpose mechanism for
supplying binding-specific details to the VIF driver.

This patch does not remove or replace the CAP_PORT_FILTER boolean
previously used in binding:capabilities. A separate patch should
implement the specific key/value pairs carried by binding:vif_details
to implement VIF security. Another patch will implement the key/value
pairs needed for SR-IOV.

The ML2 plugin now allows the bound mechanism driver to supply the
binding:vif_details dictionary content, instead of just the
CAP_PORT_FILTER boolean previously carried by the binding:capabilities
attribute.

DocImpact: Need to update portbinding extension API, but no impact on
user or administrator documentation.

Implements: blueprint vif-details
Related-Bug: 1112912
Change-Id: I34be746fcfa73c70f72b4f9add8eff3ac88c723f