classes/image: allow complementary package globs to be extended

classes/image: allow complementary package globs to be extended

Make it easy for the wildcard specifications for complementary package
features to be extended outside of image.bbclass. For example, to add a
new "foo-pkgs" item that could be added to IMAGE_FEATURES that would
cause *-foo packages to be installed for all packages currently in the
image, you can now use this line at the global level:

COMPLEMENTARY_GLOB[foo-pkgs] = "*-foo"

Implements [YOCTO #4228].

(From OE-Core rev: 4e39c1b9dbba1d2b07ffc2c6a1a252fc8f7680ee)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>