kubernetes_node_pool: fix fetching node-pool when AutoPilot is not available

[multani]

When AutoPilot is not available (not disabled), cluster.Autopilot is nil and cluster.Autopilot.Enabled crashes the plugin with a invalid memory address or nil pointer dereference error.

Integration test logs

Logs

Example query results

Results

Before the fix:

> select name, autopilot_enabled from gcp_kubernetes_cluster;
+-----------+-------------------+
| name      | autopilot_enabled |
+-----------+-------------------+
| cluster-3 | false             |
| cluster-4 | false             |
| cluster-1 | <null>            |
| cluster-2 | false             |
+-----------+-------------------+
>
> select cluster_name, name from gcp_kubernetes_node_pool where cluster_name = 'cluster-4' order by name limit 1;

Error: test_gcp: runtime error: invalid memory address or nil pointer dereference (SQLSTATE HV000)

+--------------+------+
| cluster_name | name |
+--------------+------+
+--------------+------+
>
> select cluster_name, name from gcp_kubernetes_node_pool where cluster_name = 'cluster-3' order by name limit 1;

Error: test_gcp: runtime error: invalid memory address or nil pointer dereference (SQLSTATE HV000)

+--------------+------+
| cluster_name | name |
+--------------+------+
+--------------+------+
>

After the fix:

> select name, autopilot_enabled from gcp_kubernetes_cluster;
+-----------+-------------------+
| name      | autopilot_enabled |
+-----------+-------------------+
| cluster-3 | false             |
| cluster-4 | false             |
| cluster-1 | <null>            |
| cluster-2 | false             |
+-----------+-------------------+
>
> select cluster_name, name from gcp_kubernetes_node_pool where cluster_name = 'cluster-4' order by name limit 1;
+---------------+-------------+
| cluster_name  | name        |
+---------------+-------------+
| cluster-4     | node-pool-1 |
+---------------+-------------+
>
> select cluster_name, name from gcp_kubernetes_node_pool where cluster_name = 'cluster-3' order by name limit 1;
+---------------+-------------+
| cluster_name  | name        |
+---------------+-------------+
| cluster-3     | node-pool-1 |
+---------------+-------------+
>