Separate common 'start_up' definition from v2 schema

Tempest contains API schema definitions for response checks of Nova
v2/v3 APIs. On hosts 'start_up' API, the v3 definition refers to v2
one. However, we need to avoid this kind of dependency because we will
need to change v3 definition due to this dependency when removing v2
tests.

This patch separates common 'start_up' definition from v2 schema and
moves it to common schema file.

Partially implements blueprint nova-api-attribute-test

Change-Id: If4291fcb6617b00a67066e3869deaf5a8a53f526
Merge "Separate common 'start_up' definition from v2 schema"