Import patches shipped by Ubuntu 19.10 and 20.04

These are all backports from a newer upstream version, and have been tested in Ubuntu for the most recent short term release and the soon-to-be-released 20.04 LTS.

@mtmiller patches imported from https://launchpad.net/ubuntu/+source/network-manager-openconnect with the exception of the sigint/sigterm one, which we already backported ourselves in experimental.