gn2bp: fix script location

Remove leading '//' and add '$(location)' marker for action script.

Test: //base:base
Change-Id: I8936d9d162d1f729fd9a70b3aac4b4b5fb57525a
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index 981a6a9..46caec4 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -671,10 +671,11 @@
 def create_action_module(blueprint, target):
   bp_module_name = label_to_module_name(target.name)
   module = Module('genrule', bp_module_name, target.name)
-  module.tool_files = [target.script]
+  script = gn_utils.label_to_path(target.script)
+  module.tool_files = [script]
 
   arg_string = ' '.join(target.args)
-  module.cmd = '%s %s' % (target.script, arg_string)
+  module.cmd = '$(location %s) %s' % (script, arg_string)
 
   # TODO: is this correct?
   module.tool_files.extend(':' + label_to_module_name(it) for it in target.deps)