Only the env variables which were added to the datastore were being
updated. We need to update the whole copy, we just only trigger a
reparse if any of the variables making it into the datastore change.
This avoids a bug where variables such as DISPLAY in a new UI context
would break under memory resident bitbake.
(Bitbake rev: 4bb71b627767297269e762b414443e15e28bfac4)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>