Netkvm: Fix session handling issue during netkvm driver installation

[heywji]

During acceptance testing, installing the netkvm driver on an existing network interface caused session handling issues, leading to test failures. This patch changes the session handling from SSH to serial session by replacing vm.wait_for_login() with vm.wait_for_serial_login() . It also adds a ping test to verify network connectivity after the driver installation.

ID: 1382 Signed-off-by: wji [email protected]