User session removal changes broke Yocto autobuilder testing

In my rework to remove the systemd user session, I included some tweaks to pull in polkit for weston and agl-compositor when it is in DISTRO_FEATURES.  This broke testing on the autobuilder since it does the test build with just poky and meta-agl-core and uses our poky-agl distro configuration.  That means polkit is in DISTRO_FEATURES, but polkit is unavailable due to meta-oe not being in the layer stack, so boom.  Since it is my understanding that we do not want to make meta-oe a hard requirement for using meta-agl-core, some rework is required to fix this oversight and get the upstream autobuilder testing working again.