Define buildroot properly (reverted)

bin/cbuildbot.py

Index: bin/cbuildbot.py
diff --git a/bin/cbuildbot.py b/bin/cbuildbot.py
index b0a26af94cf6d5ab5e268472adc22ab3b94d512d..c255f2f7e0204a7c25c7e498fbe7e1fd4b78035a 100755
--- a/bin/cbuildbot.py
+++ b/bin/cbuildbot.py
@@ -459,7 +459,7 @@ def _GetConfig(config_name):
   return buildconfig
 
 
-def ResolveOverlays(overlays):
+def ResolveOverlays(buildroot, overlays):
   """Return the list of overlays to use for a given buildbot.
 
   Args:
@@ -521,7 +521,7 @@ def main():
     sys.exit(1)
 
   # Calculate list of overlay directories.
-  overlays = ResolveOverlays(buildconfig['overlays'])
+  overlays = ResolveOverlays(buildroot, buildconfig['overlays'])
 
   try:
     _PreFlightRinse(buildroot, buildconfig['board'], tracking_branch, overlays)