vxlan: add vxlan tests
vxlan_do_not_up_if_no_master: Check that NM doesn't up a vlan profile if there is no master.
https://bugzilla.redhat.com/show_bug.cgi?id=1774074
vxlan_libnm_shows_port_numbers: Check that libnm (nmclient) can return port numbers correctly. Two helpers for getting properties from device and connection were added to be used with other tests.
Edited by Vladimír Beneš