Fresh Tumbleweed install, when trying to establish connection to a WPA-PSK
protected WLAN network the 'yast2 lan' tool exits silently, the wireless
interface stays down with no apparent effect. The only symptom/indication
(besides the lack of connection) of the things not going right is the error of
the wicked systemd service in the form of ���WIRELESS_WPA_PSK value not
specified'.

The solution/workaround is to manually add the WIRELESS_WPA_PSK='passphrase'
line to the wireless interface wicked configuration file at
'/etc/sysconfig/network/ifcfg-wlp4s0' followed by the restart of thw wicked
systemd service. If at any time after that the 'yast2 lan' tool is used again
the line disappears from the file and the procedure need to be repeated.

This issue was briefly discussed in the forum at:

https://forums.opensuse.org/showthread.php/538061-Wicked-can-t-connect-WLAN-WIRELESS_WPA_PSK-value-not-specified-systemd-wicked-unit-error?p=2918607