Update test with new vm.save_to_file behavior

[pevogam]

The pull request avocado-framework/avocado-vt#3519 will unify the behavior of ram to file migrations for a qemu vm. In particular, we will have to update this test

tp-qemu/qemu/tests/save_restore_vm.py

Lines 43 to 44 in 19113f9

	vm.restore_from_file(save_file)
	session = vm.wait_for_login(timeout=timeout)

as per comment

avocado-framework/avocado-vt#3519 (comment)