The changing of the environment inside the wget fetcher can race if
threading is used, such as with sstate in OE-Core. Abstract the function
so the environment can be correct before the function is called, removing
the race since the enviroment is then no longer changed.
(Bitbake rev: c73bb6023c73f003a160bb02aa4da1b580b86c23)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>