Set cmd paths in udev rules using --prefix

Set cmd paths in udev rules using --prefix

The udev/rules.d scripts must use absolute paths to their support
binaries.  However, where those binaries get installed depends
on what --prefix was set to when the package was configured.
This change makes the udev/rules.d helpers to *.in files which
are processed by configure.  This allows them to be dynamically
updated to include the specified --prefix.

Additionally, this change updates 60-zvol.rules to handle both
the 'add' and 'change' actions.  This ensures that that all
valid zvol devices are correctly linked.