net/dhcp: raise InvalidDHCPLeaseFileError on error parsing dhcpcd lease

[cjp256]

Seeing a fairly large number of lease parsing failures on Azure similar to:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/cloudinit/sources/DataSourceAzure.py", line 851, in _get_data
    crawled_data = util.log_time(
                   ^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/util.py", line 2828, in log_time
    ret = func(*args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/sources/helpers/azure.py", line 45, in impl
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/sources/DataSourceAzure.py", line 660, in crawl_metadata
    self._wait_for_pps_savable_reuse()
  File "/usr/lib/python3/dist-packages/cloudinit/sources/helpers/azure.py", line 45, in impl
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/sources/DataSourceAzure.py", line 1236, in _wait_for_pps_savable_reuse
    self._wait_for_hot_attached_primary_nic(nl_sock)
  File "/usr/lib/python3/dist-packages/cloudinit/sources/helpers/azure.py", line 45, in impl
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/sources/DataSourceAzure.py", line 1142, in _wait_for_hot_attached_primary_nic
    primary_nic_found = self._setup_ephemeral_networking(
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/sources/helpers/azure.py", line 45, in impl
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/sources/DataSourceAzure.py", line 440, in _setup_ephemeral_networking
    lease = self._ephemeral_dhcp_ctx.obtain_lease()
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/net/ephemeral.py", line 293, in obtain_lease
    self.lease = maybe_perform_dhcp_discovery(
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/net/dhcp.py", line 103, in maybe_perform_dhcp_discovery
    return distro.dhcp_client.dhcp_discovery(interface, dhcp_log_func, distro)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/net/dhcp.py", line 656, in dhcp_discovery
    lease = self.get_newest_lease(interface)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/net/dhcp.py", line 829, in get_newest_lease
    return self.parse_dhcpcd_lease(
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/cloudinit/net/dhcp.py", line 787, in parse_dhcpcd_lease
    lease = dict(
            ^^^^^
ValueError: dictionary update sequence element #0 has length 1; 2 is required

Catch this error in parse_dhcpcd_lease() and raise InvalidDHCPLeaseFileError after logging an error.

[cjp256]

I will be happy to come back and add unit test coverage in a separate PR after I get some samples of what actually went wrong.

[holmanb]

@cjp256 Thanks for this PR. I hadn't seen this during testing.

Seeing what dhcpcd actually returns when this occurs would be really useful. I think that this is the right exception to raise when parsing fails, and I'll add a followup PR to make the parsing more robust to unexpected input.

[holmanb]

Just need to fix ruff/black CI failures then this can land.

[holmanb]

@cjp256 I just filed a follow-up PR based on this branch which makes parsing more robust.

[cjp256]

@holmanb I fixed the tests and moved the debug dump of the lease up to the top level to help debug other unforeseen cases.

[anhvoms]

LGTM!