useradd: Ensure preinst data is expanded correctly in pkgdata

The preinst data in pkgdata will not expand out the ${XXX_PARAM} variables
since they don't use a package suffix. It happens that the final expansion
used for the packages is corrected by a second trip through the datastore.

The first version is used for calculation of the task output hash and
recent improvements in hash reuse showed this data wasn't using included
in the hashes, meaning for example builds with dynamic IDs were mixing
sstate with builds using static IDs. The result was a mess.

Fix this by expanding the data in the preinst correctly to use the
package specific _PARAM values.

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