Add code for creating qemu image on server side

Ref https://github.com/GNS3/gns3-gui/issues/558

tests/modules/qemu/test_qemu_vm.py

@@ -408,3 +408,50 @@ def test_options(vm):
     vm.options = "-usb"
     assert vm.options == "-usb"
     assert vm.kvm is False
+
+
+def test_get_qemu_img(vm, tmpdir):
+
+    open(str(tmpdir / "qemu-sytem-x86_64"), "w+").close()
+    open(str(tmpdir / "qemu-img"), "w+").close()
+    vm._qemu_path = str(tmpdir / "qemu-sytem-x86_64")
+    assert vm._get_qemu_img() ==  str(tmpdir / "qemu-img")
+
+
+def test_get_qemu_img_not_exist(vm, tmpdir):
+
+    open(str(tmpdir / "qemu-sytem-x86_64"), "w+").close()
+    vm._qemu_path = str(tmpdir / "qemu-sytem-x86_64")
+    with pytest.raises(QemuError):
+        vm._get_qemu_img()
+
+
+def test_create_image(vm, loop, fake_qemu_img_binary):
+    options = {
+        "type": "qcow2",
+        "preallocation": "metadata",
+        "cluster_size": 64,
+        "refcount_bits": 12,
+        "lazy_refcounts": "off",
+        "size": 100
+    }
+    with asyncio_patch("asyncio.create_subprocess_exec", return_value=MagicMock()) as process:
+        filename = loop.run_until_complete(asyncio.async(vm._create_disk("hda", options)))
+        args, kwargs = process.call_args
+        assert args == (
+            fake_qemu_img_binary,
+            "create",
+            "-f",
+            "qcow2",
+            "-o",
+            "cluster_size=64",
+            "-o",
+            "lazy_refcounts=off",
+            "-o",
+            "preallocation=metadata",
+            "-o",
+            "refcount_bits=12",
+            os.path.join(vm.working_dir, "hda.qcow2"),
+            "100M"
+        )
+    assert filename == "hda.qcow2"