wic: use Filesystem UUID when expand swap partition

part.get("uuid") return the Partition UUID from the partition
table instead of Filesystem UUID. This lead to swap partition
UUID not match/change when wic write expand swap partition.

change it to read the filesystem UUID using blkid. The output
from blkid should looks like this:
wic-partvzhiwq3s: LABEL="swap1" UUID="04e55c19-3f3f-4491-9e32-44eea8daa827" VERSION="1" TYPE="swap" USAGE="other"

[YOCTO #13313]

Signed-off-by: Lee Chee Yang <chee.yang.lee@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>