Do not hardcode path separators in build paths.

Do not hardcode path separators in build paths.

It is conceivable that iotivity may be built on platforms where '/'
is not a suitable directory separator.  When constructing paths use
Python's os.path.join() function instead of constructing paths by
concatenating strings with '/' in them.

Change-Id: I7c435bd454339f4df9a8e41250e705aa98a6d09f
Signed-off-by: Ossama Othman <ossama.othman@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/456
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Erich Keane <erich.keane@intel.com>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>