Check if temperature sensor on Cisco device is not supported

Some older Cisco devices like models from the 2960 platform have no temperature sensor built-in. In that case the get_environment function will throw on exception. That case will now be handeled.

napalm/ios/ios.py

@@ -2110,7 +2110,7 @@ def get_environment(self):
         re_temp_value = re.compile("(.*) Temperature Value")
         # The 'show env temperature status' is not ubiquitous in Cisco IOS
         output = self._send_command(temp_cmd)
-        if "% Invalid" not in output:
+        if "% Invalid" and "Not Supported" not in output:
             for line in output.splitlines():
                 m = re_temp_value.match(line)
                 if m is not None: