vdev_id support for device link aliases

Add a vdev_id feature to map device names based on already defined
udev device links. To increase the odds that vdev_id will run after
the rules it depends on, increase the vdev.rules rule number from 60
to 69. With this change, vdev_id now provides functionality analogous
to zpool_id and zpool_layout, paving the way to retire those tools.

A defined alias takes precedence over a topology-derived name, but the
two naming methods can otherwise coexist. For example, one might name
drives in a JBOD with the sas_direct topology while naming an internal
L2ARC device with an alias.

For example, the following lines in vdev_id.conf will result in the
creation of links /dev/disk/by-vdev/{d1,d2}, each pointing to the same
target as the device link specified in the third field.

1. by-vdev
2. name fully qualified or base name of device link alias d1 /dev/disk/by-id/wwn-0x5000c5002de3b9ca alias d2 wwn-0x5000c5002def789e

Also perform some minor vdev_id cleanup, such as removal of the unused
-s command line option.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #981