layerman: disable meta-opie

Parsing recipes...ERROR: Please ensure recipe
/build/jenkins/angstrom-v2014.12/machine/raspberrypi/sources/meta-opie/recipes-opie/packagegroups/packagegroup-opie-16mb.bb
sets PACKAGE_ARCH before inherit packagegroup
ERROR: Please ensure recipe
/build/jenkins/angstrom-v2014.12/machine/raspberrypi/sources/meta-opie/recipes-opie/packagegroups/packagegroup-opie.bb
sets PACKAGE_ARCH before inherit packagegroup

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>