GNU Patch < 2.6.1 has a race condition so we create a per-instance TMPDIR to
avoid this. This was implemented by setting os.environ[TMPDIR] but at the end
of do_patch the temporary directory is deleted but TMPDIR is not unset.
In general this doesn't cause a problem but if do_patch is embedded in a larger
function then TMPDIR is set to a directory that doesn't exist. Avoid this by
removing TMPDIR from os.environ when the directory is deleted.
Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
