parse links retrieved from rd, move server thread into CoapServer, add tests

• linux/VirtualizationReceiver: MockEddieResource now stores data which is accessed by get/post/put requests
• parse links from resource directory response and return std::vector<Link> from get_resources_from_rd
• zephyr: implement request timeout
• add tests for requests and response
• add tests that send requests to discovered resources
• CoapServer's start_server() method now starts the server in a non-blocking separate thread

See git history for more details

Signed-off-by: Francesco Pham francesco.pham@huawei.com