udev: Effectively revert the move to /sbin

This effectively reverts the changes made in b49ddeb11c0319b7ece278fd7cef6b0223114ca9
to move udev's libexecdir to sbin. The changes caused too many issues in
other plaves and were not well enough tested this close to a release.

Rather than use base_libdir, the nonarch version is used to try and give some
chance of multilib not being totally broken in the release.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
packagegroup: Add init-manager sanity check

Currently, you can set VIRTUAL-RUNTIME_init_manager to an init system that
isn't in DISTRO_FEATURES. This leads to head scratching over unbootable images.

This adds a sanity check which ensures more valid systems are built.

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