packagegroup-rpb: use bb.utils.contains to filter out docker
packagegroup-rpb: use bb.utils.contains to filter out docker

The current approach prevents to use:
 RDEPENDS_packagegroup-rpb_remove = "docker"

It's causing the following error:
 Computing transaction...error: Can't install packagegroup-rpb-1.0-r0@all:
 no package provides docker

Use bitbake's utils.contains function to filter out docker, instead of the
current approach and allow to use RDEPENDS_packagegroup-rpb.

Signed-off-by: Fathi Boudra <7cd6e55cc07a66bc71d7901a4cddfe6c22aab659@linaro.org>

fboudra/meta-rpb,96boards/meta-rpb,fboudra/meta-rpb,96boards/meta-rpb,fboudra/meta-rpb