Initial hotplug support (#936)

Adds a udev script which will invoke a hotplug hook script on all net
add events. The script will write some udev arguments to a systemd FIFO
socket (to ensure we have only instance of cloud-init running at a
time), which is then read by a new service that calls a new 'cloud-init
devel hotplug-hook' command to handle the new event.

This hotplug-hook command will:
- Fetch the pickled datsource
- Verify that the hotplug event is supported/enabled
- Update the metadata for the datasource
- Ensure the hotplugged device exists within the datasource
- Apply the config change on the datasource metadata
- Bring up the new interface (or apply global network configuration)
- Save the updated metadata back to the pickle cache

Also scattered in some unrelated typing where helpful

1 files changed, 2 insertions, 1 deletions

diff --git a/cloudinit/sources/__init__.py b/cloudinit/sources/__init__.py
index 9d25b0ee..bf6bf139 100644
--- a/cloudinit/sources/__init__.py
+++ b/cloudinit/sources/__init__.py
@@ -23,6 +23,7 @@ from cloudinit import type_utils
 from cloudinit import user_data as ud
 from cloudinit import util
 from cloudinit.atomic_helper import write_json
+from cloudinit.distros import Distro
 from cloudinit.event import EventScope, EventType
 from cloudinit.filters import launch_index
 from cloudinit.persistence import CloudInitPickleMixin
@@ -215,7 +216,7 @@ class DataSource(CloudInitPickleMixin, metaclass=abc.ABCMeta):
 
     _ci_pkl_version = 1
 
-    def __init__(self, sys_cfg, distro, paths, ud_proc=None):
+    def __init__(self, sys_cfg, distro: Distro, paths, ud_proc=None):
         self.sys_cfg = sys_cfg
         self.distro = distro
         self.paths = paths