The parsing shutdown call can occur more than once. Currently
if this happens the code will hang. Add some code to prevent this.
[YOCTO #2039 partial]
(Bitbake rev: 7614c5bdcaf9d70614b4fad2ca02c7e6eaa92f1b)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>