Move the swagger api submodule to mgmt

This remove the swagger API submodule and add its files under the mgmt
submodule, under the same directory name.

The Makefile no longer needs to pull the submodule.

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>