Comment 12 for bug 1711760

Your /run does not have a /run/initramfs/open-iscsi.interface file
that file should have been written by the initramfs local-top code.
if it is not present, then resolvconf will not be run by
net-interface-handler [1] and /etc/resolv.conf not updated.

I'm not sure how that could have happened though.
the code that does this is at [2]

[1] https://git.launchpad.net/~usd-import-team/ubuntu/+source/open-iscsi/tree/debian/net-interface-handler?h=applied/ubuntu/xenial-devel
[2] https://git.launchpad.net/~usd-import-team/ubuntu/+source/open-iscsi/tree/debian/extra/initramfs.local-top?h=applied/ubuntu/xenial-devel#n181