Fix importing key-direction from *.ovpn files

Summary:
It is possible for key-direction to be specified *after* <tls-auth>.
Previously the code always expected it to be defined before, with this
change *.ovpn files that define it after should also be imported correctly.

Reviewers: jgrulich!

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D29781