feat: switch off the fix templates QTS cannot take (0.4.0)

napalm-linux 0.8 implements napalm-device-types' fix templates. QTS has
no apt, dnf or opkg and sets its SNMP agent in its own UI, so
configure_snmp_agent, configure_package_proxy and ensure_package are
None here: a capability check answers no instead of offering a fix
that fails, as the inherited fix_snmp and fix_apt_proxy did.

get_device_warnings returns nothing: the inherited one asked for
updates, which is None here, and logged a TypeError on every poll.

The role test follows napalm-linux's get_os_users.

Closes #6. Part of #7.

napalm_qnap_qts/qnap_qts.py

@@ -78,6 +78,15 @@ class QnapQtsDriver(StorageDriver, HypervisorDriver, LinuxDriver):
     get_available_updates = None  # type: ignore[assignment]
     refresh_available_updates = None  # type: ignore[assignment]
     apply_updates = None  # type: ignore[assignment]
+    #: The fix templates LinuxDriver carries need a package manager or net-snmp
+    #: from packages; QTS has neither, and its SNMP agent is set in its own UI.
+    configure_snmp_agent = None  # type: ignore[assignment]
+    configure_package_proxy = None  # type: ignore[assignment]
+    ensure_package = None  # type: ignore[assignment]
+
+    def get_device_warnings(self) -> list:
+        """Nothing to report: the inherited one asks for updates QTS cannot list."""
+        return []
 
     SNMP_OBJECT_ID_PREFIX = QNAP_ENTERPRISE_OID
     SNMP_FINGERPRINT = [