rapidjson: Add prepare scriptlet

rapidjson: Add prepare scriptlet

It is strongly recommended to rely on scons,
if not possible, this can be done differently using this script.

For more details about building IoTivity please check:

https://wiki.iotivity.org/build

The main purpose of prep.sh, is for continuous integration experiments
 for Tizen platform, but could be used for others too.

Bug: https://jira.iotivity.org/browse/IOT-1600
Change-Id: I8b07fdc4762baf403079c8816fc3017372627ef7
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/17537
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>