oe.packagegroup: add code for package groups (sync from OE)

This includes some utility functions for dealing with groups of packages
defined in the metadata.  Metadata syntax:

    PACKAGE_GROUP_<group> = "<list of packages>"

If the packages in the group are optional:

    PACKAGE_GROUP_<group>[optional] = "1"

(From OE-Core rev: 4df212e9c2a1dd7c80d180fd13b67e9f2799d3e1)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/base.bbclass

@@ -10,7 +10,7 @@ inherit metadata_scm
 inherit buildstats
 inherit logging
 
-OE_IMPORTS += "os sys time oe.path oe.utils oe.data"
+OE_IMPORTS += "os sys time oe.path oe.utils oe.data oe.packagegroup"
 OE_IMPORTS[type] = "list"
 
 def oe_import(d):

meta/lib/oe/packagegroup.py

@@ -0,0 +1,29 @@
+import itertools
+
+def is_optional(group, d):
+    return bool(d.getVarFlag("PACKAGE_GROUP_%s" % group, "optional"))
+
+def packages(groups, d):
+    for group in groups:
+        for pkg in (d.getVar("PACKAGE_GROUP_%s" % group, True) or "").split():
+            yield pkg
+
+def required_packages(groups, d):
+    req = filter(lambda group: not is_optional(group, d), groups)
+    return packages(req, d)
+
+def optional_packages(groups, d):
+    opt = filter(lambda group: is_optional(group, d), groups)
+    return packages(opt, d)
+
+def active_packages(features, d):
+    return itertools.chain(required_packages(features, d),
+                           optional_packages(features, d))
+
+def active_recipes(features, d):
+    import oe.packagedata
+
+    for pkg in active_packages(features, d):
+        recipe = oe.packagedata.recipename(pkg, d)
+        if recipe:
+            yield recipe