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, 1 insertions, 0 deletions

diff --git a/cloudinit/event.py b/cloudinit/event.py
index 76a0afc6..53ad4c25 100644
--- a/cloudinit/event.py
+++ b/cloudinit/event.py
@@ -29,6 +29,7 @@ class EventType(Enum):
     BOOT = "boot"
     BOOT_NEW_INSTANCE = "boot-new-instance"
     BOOT_LEGACY = "boot-legacy"
+    HOTPLUG = 'hotplug'
 
     def __str__(self):  # pylint: disable=invalid-str-returned
         return self.value