Add "body=" argument to v3 API unit tests

This patch adds "body=" argument to v3 API unit tests for avoiding
the test failures due to KeyError when applying the API validation
framework to "create a server" API.

_process_stack() of nova's wsgi passes kwargs which includes 'body'
like:
    {'body': {u'server': {u'name': u'my-server', [..]}}}
to an API method. The validation framework finds a body with the
keyword 'body' from the kwargs, and validates the body with the API
schema. So this changes is also for fitting the arguments to the wsgi
behavior.

Partially implements blueprint nova-api-validation-fw

Change-Id: Id5fa416e021b529e20aca3701e3f159bb316e7fb
Merge "Add "body=" argument to v3 API unit tests"