utils.bbclass: fix is_machine_specific

utils.bbclass: fix is_machine_specific

* base.bbclass can set a package's PACKAGE_ARCH to MACHINE_ARCH if
it finds file:// in the SRC_URI and the corresponding file is machine
specific (recipes/foo/foo-1.0/<some machine>/)
* but is_machine_specific actually fails to detect these files as
urldata.path is used instead of urldata.localpath thus preventing the
comparison of the file's path with machinepaths
* tested with bitbake HEAD & 1.8.18, with OE's tree alone and OE's tree
plus an overlay.

Signed-off-by: Eric Bénard <eric@eukrea.com>
Acked-by: Chris Larson <clarson@kergoth.com>
Acked-by: Khem Raj <raj.khem@gmail.com>