hob: adding INHERIT += " testimage " affects image recipes list

To find if a recipe is for an image, Hob checks if it inherits
image.bbclass. But when you add testimage in local.conf, this will
be added for each recipe, and it pass the test. Adding a "/" before
"image.bbclass", will check only for image.bbclass.

[YOCTO #6117]
Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
hob: fix customization of empty image recipe

This fixes a problem which happened when you tried to build an
image by selecting 'Start with an empty image recipe' from the
Image configuration page of hob.

The reason on of the bug was that the name of the resulting image
was threated the same way as ordinary custom images, when in fact
they should use the default name: "hob-image", because they do not
derive from any other recipe.

[YOCTO #6102]

Signed-off-by: Marius Avram <marius.avram@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>