I'm using ArchLinux with Plasma 5.9.2

I got this error while installing Look and Feel packages

```
    Feb 21 13:27:05 FredArch kcmshell5[1200]: org.kde.kcoreaddons: Error loading plugin "kcm_lookandfeel" "The shared library was not found." 
    Plugin search paths are ("/usr/lib/qt/plugins", "/usr/bin") 
    The environment variable QT_PLUGIN_PATH might be not correctly set
```

The file kcm_lookandfeel.so is installed to /usr/lib/qt/plugins/kcms whereas most of other kcm_*.so's are located in /usr/lib/qt/plugins

In https://github.com/KDE/plasma-desktop/blob/48db84cf1b2c6dc78a19419e4b37c5630b465ef6/kcms/lookandfeel/CMakeLists.txt#L51, it explicitly specifies the sub-directory.

Some other files in the sub-directory:
ll /usr/lib/qt/plugins/kcms
total 564K
drwxr-xr-x  2 root root 4.0K Feb 22 00:52 .
drwxr-xr-x 44 root root  12K Feb 22 00:52 ..
-rwxr-xr-x  1 root root  64K Feb 15 03:36 kcm_desktoptheme.so
-rwxr-xr-x  1 root root 116K Feb 15 03:30 kcm_energyinfo.so
-rwxr-xr-x  1 root root  27K Feb 15 03:30 kcm_fileindexermonitor.so
-rwxr-xr-x  1 root root 189K Feb 15 03:36 kcm_lookandfeel.so
-rwxr-xr-x  1 root root  71K Dec 19 04:02 kcm_pointingdevices.so
-rwxr-xr-x  1 root root  27K Feb 15 03:38 kcm_pulseaudio.so
-rwxr-xr-x  1 root root  47K Feb 15 03:36 kcm_splashscreen.so