ptest bug fixes

ptest bug fixes

Move ${PN}-ptest to start of PACKAGES to ensure all ptest files are
packaged in the -ptest package.

Add QA exclusions to insane.bbclass to ensure -ptest packages can contain
any files they need.

Disable ptest for native packages.

Don't emit errors on missing _ptest functions.

Signed-off-by: Björn Stenberg <bjst@enea.com>
Signed-off-by: Anders Roxell <anders.roxell@enea.com>
Signed-off-by: Josep Puigdemont <josep.puigdemont@enea.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>