Fix remaining problems with nmcli v0.9.10

This takes care of the remaining concerns raised in #75 (which completes the fixes required for #74). The commit messages provide explanations for these changes.

Please test that 10641b4f05f7f477567e628d58d016cf7b7848e2 doesn't break restarting the network connection on older versions of `nmcli`. (IIRC, the line removed by this commit was never necessary, but I'm not entirely sure.)