wic: fix wrong attempt to create file system in upartitioned regions

wic: fix wrong attempt to create file system in upartitioned regions

The kickstart parser defaults fstype to "vfat". This leads to an attempt
to create an empty file system even for regions configured with "--no-table"
if used without fstype when no --sourceparams given.

The fix tests for fstype "none" or no_table in Partition prepare method.
This will omit the file system creation an the potential error for small
region with --no-table option.

Signed-off-by: Markus Niebel <Markus.Niebel@ew.tq-group.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit db771a4cd36bf291a8b68edfd905e03243f2c8b3)
Signed-off-by: Steve Sakoman <steve@sakoman.com>