cloud-init threw an exception after replacing a NIC which belongs to provisioning network.

Issue

• cloud-init threw an exception after replacing a NIC which belongs to provisioning network.

   util.py[DEBUG]: Reading from /sys/class/net/ens3/type (quiet=False)
   util.py[DEBUG]: Read 2 bytes from /sys/class/net/ens3/type
   util.py[WARNING]: failed stage init
   util.py[DEBUG]: failed stage init
  Traceback (most recent call last):
    File "/usr/lib/python3.6/site-packages/cloudinit/cmd/main.py", line 653, in status_wrapper
      ret = functor(name, args)
    File "/usr/lib/python3.6/site-packages/cloudinit/cmd/main.py", line 362, in main_init
      init.apply_network_config(bring_up=bool(mode != sources.DSMODE_LOCAL))
    File "/usr/lib/python3.6/site-packages/cloudinit/stages.py", line 681, in apply_network_config
      netcfg, src = self._find_networking_config()
    File "/usr/lib/python3.6/site-packages/cloudinit/stages.py", line 646, in _find_networking_config
      if self.datasource and hasattr(self.datasource, 'network_config'):
    File "/usr/lib/python3.6/site-packages/cloudinit/sources/DataSourceConfigDrive.py", line 152, in network_config
      self.network_json, known_macs=self.known_macs)
    File "/usr/lib/python3.6/site-packages/cloudinit/sources/helpers/openstack.py", line 683, in convert_net_json
      raise ValueError("Unable to find a system nic for %s" % d)
  ValueError: Unable to find a system nic for {'type': 'physical', 'mtu': 1500, 'subnets': [{'type': 'dhcp4'}], 'mac_address': '<old MAC address>'}
   atomic_helper.py[DEBUG]: Atomically writing to file /var/lib/cloud/data/status.json (via temporary file /var/lib/cloud/data/tmpm9hc8a2w) - w: [644] 790 bytes/chars
   util.py[DEBUG]: Reading from /proc/uptime (quiet=False)
   util.py[DEBUG]: Read 13 bytes from /proc/uptime
   util.py[DEBUG]: cloud-init mode 'init' took 0.124 seconds