oeqa/runtime: rpm: fix finding the test rpm file

oeqa/runtime: rpm: fix finding the test rpm file

Translate TUNE_PKGARCH to find the right file (this
used to work because tune for qemux86-64 used to be
x86_64 now it's core2-64)
Also, while using packagedata was nice, it's harder to make
the test exportable and runnable outside of the
build system. (where oe.packagedata isn't available)

(From OE-Core rev: fd0e9ad4d295ca11b33c3e3e11069421dee834e8)

Signed-off-by: Stefan Stanacar <stefanx.stanacar@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>