Add API schema for v2.1/v3 remote_consoles API

By defining the API schema, it is possible to separate the validation
code from the API method. The API method can be more simple.
In addition, a response of API validation error can be consistent for
the whole Nova API.

Partially implements blueprint v3-api-schema

Change-Id: Icdb1f87903e3c4345e6533c08b2f2d2f9d36316e
libvirt: add '_' prefix to some get_host_* methods

The get_host_uuid, get_host_capabilities and get_host_cpu_for_guest
methods are all internal helpers so should have a '_' prefix to
indicate they are not part of public virt driver API.

Related-bug: #1333219
Change-Id: Ice22f52ef1f4ec0b950b5fdf303499ea5c2ba7be
Merge "libvirt: add '_' prefix to some get_host_* methods"
Merge "Add API schema for v2.1/v3 remote_consoles API"