insane.bbclass: Added QA test for expanded ${D}

Checks in FILES and pkg_* variables, solves common mistake of

using ${D} instead of $D and warns the user accordingly.

[YOCTO #6642]

Signed-off-by: Alejandro Hernandez <alejandro.hernandez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>