insane.bbclass: Add pkgvarcheck to check for suboptimal usages of variables

insane.bbclass: Add pkgvarcheck to check for suboptimal usages of variables

Check through the variables:
'RDEPENDS', 'RRECOMMENDS', 'FILES', 'pkg_preinst', 'pkg_postinst', 'pkg_prerm', 'pkg_postrm'
and if there is a variable set which isn't package specific, inform the user
of this.

Using these variables without a package suffix is bad practise and complicates
dependencies of packages unnecessarily as well as complicates the code. Lets
convert the remaining issues and then we can take the small performance gain.

(From OE-Core rev: 316228948e65f376f6c5be13ccd0c964ea630edf)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>