Set proper default NIC of network_check_list

Default NIC of network_check_list is eth0 which is barely used and
always caused maas checks to fail. Now We only need to worry the
 state of bond interface. This change covers most of practical
  customer cases.

Connects:#742

rpcd/playbooks/roles/rpc_maas/defaults/main.yml

@@ -358,7 +358,7 @@ ceph_checks_list:
   - { name: "ceph_cluster_stats", group: "mons" }
 
 network_checks_list:
-  - { name: "eth0", group: "hosts", max_speed: "{{ net_max_speed }}", rx_pct_warn: "{{ net_rx_pct_warn }}", rx_pct_crit: "{{ net_rx_pct_crit }}", tx_pct_warn: "{{ net_tx_pct_warn }}", tx_pct_crit: "{{ net_tx_pct_crit }}"}
+  - { name: "{{ ansible_default_ipv4.interface }}", group: "hosts", max_speed: "{{ net_max_speed }}", rx_pct_warn: "{{ net_rx_pct_warn }}", rx_pct_crit: "{{ net_rx_pct_crit }}", tx_pct_warn: "{{ net_tx_pct_warn }}", tx_pct_crit: "{{ net_tx_pct_crit }}"}
 
 kernel_checks_list:
   - { name: "conntrack_count", group: "hosts" }