dispatcher: uuu: Allow filesystem image as rootfs

Currently, it's only possible to apply overlay on disk images(e.g. wic)
since ApplyOverlay requests (by default) a root_partition parameter.

Allow to use standard filesystem image (e.g ext4) by setting the
ApplyOverlay() use_root_partition parameter to false when there
is no root_parition defined, and so consider it as standard filesystem
image.

Change-Id: If7ed27fbdcfa13cf3141db054107e737aed15922
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
18 jobs for uuu in 17 minutes and 16 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Test
passed #108572
amd64
dispatcher-debian-10

00:02:25

passed #108574
amd64
dispatcher-debian-11

00:02:38

passed #108573
amd64
server-debian-10

00:02:48

passed #108575
amd64
server-debian-11

00:05:20

 
  Analyze
canceled #108704
amd64-dind allowed to fail
bandit-sast

passed #108577
amd64
black

00:00:30

passed #108578
amd64
code_quality

00:00:19

passed #108579
amd64
coverage

00:06:12

59.35%
passed #108580
amd64
dockerfiles

00:00:14

passed #108582
amd64
pylint

00:02:52

passed #108581
amd64
schemas

00:00:26

failed #108576
amd64-dind allowed to fail
bandit-sast

 
  Build
passed #108584
amd64
debian/10

00:01:04

passed #108583
amd64
doc

00:00:38

passed #108687
amd64-dind
docker-amd64-dispatcher

00:04:29

passed #108705
amd64-dind
docker-amd64-server

00:04:37

failed #108585
amd64-dind
docker-amd64-dispatcher

failed #108586
amd64-dind
docker-amd64-server