MyBS: Workaround for kernel-obs-build build failure
    (JSC-SLE#5501, boo#1211226, bsc#1218184)
    
    kernel-obs-build needs root for build. This is in some way enabled for
    the package link case but not for multibuild case. As a workaround add
    the allowrootforbuild flag to prjconf for multibuild.