Fix hardcoded library path in xwalk script and Service dbus File

The binary xwalk is stored in 32 bit arch platform in /usr/lib/xwalk/xwalk
and for X64 arch in /usr/lib64/xwalk/xwalk

Adjust the paths in the launcher script and the D-BUS service file so that they point to the right location based on the architecture

Signed-off-by: Baptiste DURAND <baptiste.durand@open.eurogiciel.org>