feat: hand the container engine connection Container Station's docker

napalm-device-types 2.6.0 opens a host's container engine through
`open_container_engine()`, and asks the driver for the binary through
`_container_engine_binary()`. Under QTS docker is not on PATH; the hook
now returns the path `open()` already discovers, so the Engine API stream
(`<path> system dial-stdio`) and the CLI reach Container Station while
callers only pass arguments (NetOrk/netork#765).

Version 0.2.0, requires napalm-device-types >= 2.6.0 and
napalm-linux >= 0.2.0.

Refs NAPALM/napalm-device-types#17

tests/test_qnap_qts.py

@@ -184,6 +184,27 @@ class TestDockerBinDiscovery:
         assert driver._docker_bin() == "/opt/docker"
 
 
+class TestContainerEngineBinary:
+    """The container engine connection (napalm-device-types 2.6.0) reaches
+    Container Station's docker, not one on PATH: the driver decides where the
+    binary lives, and netOrk never sees it (NetOrk/netork#765)."""
+
+    def test_the_engine_binary_is_the_discovered_path(self, driver):
+        driver._docker_path = "/share/CACHEDEV1_DATA/.qpkg/container-station/bin/docker"
+        assert driver._container_engine_binary("docker") == driver._docker_path
+
+    def test_the_api_stream_runs_dial_stdio_from_that_path(self, driver):
+        driver._docker_path = "/share/CACHEDEV1_DATA/.qpkg/container-station/bin/docker"
+        opened = []
+        with patch.object(driver, "open_stream", side_effect=lambda cmd, **kw: opened.append(cmd)):
+            driver.open_container_engine("docker").open_api()
+        assert opened == [f"{driver._docker_path} system dial-stdio"]
+
+    def test_without_a_discovered_path_it_falls_back_to_plain_docker(self, driver):
+        driver._docker_path = None
+        assert driver._container_engine_binary("docker") == "docker"
+
+
 def test_services_cannot_be_controlled():
     """QTS has no systemd: the systemctl actions inherited from LinuxDriver would
     fail on every unit, so the driver says it cannot control services at all --