Additional hint for user stating when he need to remove the flash drive.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

This commit adds support to have multiple image variants in the test
cases files.

It also adds the respective image variants list relevant to each test
case.

This commit also updates the tests files and format definition files.

Signed-off-by: Luis Araujo <luis.araujo@collabora.co.uk>

This is a madantory field that specifies the deployment type of the
image where this test case can be executed.

The commit adds the image-deployment field for each test case, and it
currently can be a list with the following values: APT, OSTree, Any.

This commit also updates the tests files.

Signed-off-by: Luis Araujo <luis.araujo@collabora.co.uk>

This commit renames the image-type field to image-variant
in the test cases files.

It also updates the parser, renderer code, test_case template
and unittests files in order to use the new name.

Signed-off-by: Luis Araujo <luis.araujo@collabora.co.uk>

Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>

Add test to check proper behavior in the following circumstances:
- Power cut during an update
- USB mass storage unplug during an update
- The disk is full during an update

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>
Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>