[OE-core] build-sysroots deletes wic imagedata environment variables

[Volker Vogelhuber]

It seems like build-sysroots does clean the sysroot directories. This 
has the effect that the imagedata folder within the sysroots dir is 
removed as well. That imagedata folder is created by the 
do_rootfs_wicenv task. Unfortunately the state of the task seems not to 
be reset when calling bitbake build-sysroots. So the imagedata folder is 
not recreated anymore when one calls bitbake again with an image recipe. 
The only way to recreate it seems to call bitbake with -f parameter to 
force a taint of the hash for the do_rootfs_wicenv task.
Is there a better solution?