Rename API schema modules with removing "_schema"

The paths of API schema modules include "/schemas" and they show
API schema clearly. It is not necessary to include "_schema" in
module names. This patch renames the modules with removing "_schema"
from module names.

@validaiton.schema() takes 1 parameter, so calling it by name
is excessive. Then, this patch removes the specified argument.

By applying these changes, we can specify API schema module in one
line with @validation.schema().

Partially implements blueprint nova-api-validation-fw

Change-Id: Ia646e1c2466fa0a1418f757a48d2e6b4f84f7c98
Merge "Rename API schema modules with removing "_schema""