command|cooker: allow generating targets tree for specified pkgs

Modify the generateTargetsTree command to allow a list of packages to be
supplied by the caller, in this case we will only generate a target tree
for user requested targets rather than building a tree for the world list.

(Bitbake rev: d4e4f2ecae96e074b2ab3bb9882037af2e385fdd)

Signed-off-by: Joshua Lock <josh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cooker.py

@@ -594,12 +594,14 @@ class BBCooker:
 
         return target_tree
 
-    def generateTargetsTree(self, klass):
+    def generateTargetsTree(self, klass=None, pkgs=[]):
         """
         Generate a dependency tree of buildable targets
         Generate an event with the result
         """
-        pkgs = ['world']
+        # if the caller hasn't specified a pkgs list default to world
+        if not len(pkgs):
+            pkgs = ['world']
         # if inherited_class passed ensure all recipes which inherit the
         # specified class are included in pkgs
         if klass: