scripts: use OE_TMPDIR instead of TMPDIR external variable

scripts: use OE_TMPDIR instead of TMPDIR external variable

On OpenSUSE within an X session, TMPDIR is set to the system temporary
directory (/tmp) which is incorrect for these scripts. Thus, change
runqemu and oe-setup-rpmrepo to use OE_TMPDIR from the external
environment rather than TMPDIR.

Fixes [YOCTO #1530]

(From OE-Core rev: 4e24c10952c7a52af7f2447595fd484692d35534)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>