image.bbclass: Add basic support for PACKAGE_EXCLUDE

image.bbclass: Add basic support for PACKAGE_EXCLUDE

Add the foundation for the PACKAGE_EXCLUDE support.

As part of this work, it was noticed that the PACKAGE_INSTALL and
PACKAGE_INSTALL_ATTEMPTONLY were still using he 'normal' version for
dependencies.  This should no longer be necessary as of the change in the way
the complementary package groups (dev, dbg, ptest and others) are defined.
By making this change the dependency tree is more correct than before, and
gives the ability for manipulating PACKAGE_INSTALL and
PACKAGE_INSTALL_ATTEMPTONLY, while adjusting the dependencies at the same
time.

Warning messages will be generated if the user is trying to exclude a
package that was previously in the PACKAGE_INSTALL or
PACKAGE_INSTALL_ATTEMPTONLY variables.

(See additional commits for package manager specific support.)

Add documentation on PACKAGE_EXCLUDE and related variables.

(From OE-Core rev: 208d4d5ef7c5ead35dc27b7808f92ed377377aa4)

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>