Update import paths for changes to blueprint

Blueprint has been modified to include a canonical import path,
update soong to match.

Change-Id: If29d31afbf3bf2e6364961a66456fa5f8f738455

common/defs.go

@@ -15,7 +15,7 @@
 package common
 
 import (
-	"blueprint"
+	"github.com/google/blueprint"
 )
 
 var (