Fix the methods in all fetchers so they don't change
the current working directory of the calling process, which
could lead to "changed cwd" warnings from bitbake.
(Bitbake rev: 6aa78bf3bd1f75728209e2d01faef31cb8887333)
Signed-off-by: Matt Madison <matt@madison.systems>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>