Install basename utility into dracut initramfs

vdev_id requires the program basename when handling short aliases
defined in vdev_id.conf (those defined without a leading path), but
basename is not always available in the dracut environment. This
causes the pool device names to change when using by-vdev/ devices
or (in extreme cases) can make the pool import fail in dracut.

This commit fixes the problem by explicitly installing basename.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Steffen Müthing <steffen.muething@iwr.uni-heidelberg.de>
Closes #7562