Read lease files from dhclient and NetworkManager on Azure and CloudStack

[jlebon]

RHCOS/FCOS uses NetworkManager presently. So the logic to look for option 245 in the systemd-networkd lease file would need to be adapted to read from those lease files (/var/lib/NetworkManager on RHEL7, /var/lib/dhclient on FCOS and likely RHEL8). Might be worth investigating if NM's D-Bus API exposes this so we don't have to learn dhclient's syntax.

Though note that this is not a blocker for getting those platforms on Azure if we're comfortable relying exclusively on the fallback endpoint (#145) until this is implemented.

Related: #130

[bgilbert]

The CloudStack provider also reads networkd lease files via a call to dns_lease_key_lookup().

[lucab]

We should be now in a better position to tackle this, as at least we have a single network management stack in initramfs in both RHCOS and FCOS (NM with the internal DHCP client).

[lucab]

For reference, NM lease files do not seem to contain the DHCP option:

cat /var/lib/NetworkManager/internal-054597c7-5830-47a8-a54c-77e054ee00aa-eth0.lease 

# This is private data. Do not parse.
ADDRESS=10.1.42.5

[lucab]

To make this ticket easier to find out, this bug currently means that on Azure we have to wait for a timeout:

[  131.232431] afterburn[1103]: WARN Failed to get fabric address from DHCP: maximum number of retries (60) reached
[  131.244800] afterburn[1103]: INFO using fallback address

It it gets too annoying to have this timeout, we could try to add some smarter heuristic in Afterburn in order to directly reach the Azure hardcoded IP.