Fix OpenVPN import issue

[Daviey]

Previously, the command htb lab import would fail. This is because it was writing an empty file, as the write() would be buffered and not flush to file before the nmcli import was called.

This change explicitly calls flush() to commit the changes to the file, meaning the contents is written to the file.

Fixes: calebstewart/python-htb#6 Signed-off-by: Dave Walker (Daviey) [email protected]