azure: detect vnet migration via netlink media change event
Replace Azure pre-provision polling on IMDS with a blocking call
which watches for netlink link state change messages. The media
change event happens when a pre-provisioned VM has been activated
and is connected to the users virtual network and cloud-init can
then resume operation to complete image instantiation.
OVF: identify label iso9660 filesystems with label 'OVF ENV'.
When deploying an OVA, at least some versions of vmware
attach a cdrom with an ISO9660 filesystem label of 'OVF ENV'.
This was seen on Vmware vCenter Server, 6.0.0, 2776510.
In order to accomplish this we had to change the content of
the DI_ISO9660_DEVS variable to be comma delimited rather
than space delimited.
net: Ephemeral*Network: add connectivity check via URL
We add a new Optional parameter: connectivity_url
This is used in __enter__ to verify if a connection already exists.
If it does exist, no operations are performed.
azure: _poll_imds only retry on 404. Fail on Timeout
Upon URL timeout, _poll_imds is expected to re-dhcp to get updated
IP configuration. We don't want to indefinitely retry because the
instance likely has invalid IP configuration.