bitbake: hob/packageselectionpage: "Cancel" button returns to "Image configuration...

bitbake: hob/packageselectionpage: "Cancel" button returns to "Image configuration" screen

Once package building completes, you can customise the list of
packages that will go into the final image. Once you have made
the changes you need, you can either build your image, or you
can exit the process and go back to the 'Image configuration'
screen by selecting 'Cancel'.

[YOCTO #3105]
(Bitbake rev: c5fd1824c9794923576ec1e747536c0430542fd1)

Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>