There is a potential race over the mirror tarballs where a partial git repo
could be extracted causing fetcher failures if the tarball is being rewritten
whilst another build accesses it.
Create the mirror tarball atomically to avoid this.
[YOCTO #14441]
(Bitbake rev: 3250bc950c56bd7dd2114df26e5a8e13b04ceac8)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>