RUBiS workload revisited (fully compliant)

Hello,

The current implementation of the RUBiS workload only supports the Java version of [OW2 RUBiS](http://rubis.ow2.org/).
Also, only a subset of the 27 possible operations are implemented.

So I've decided to update (actually, to rewrite) it in order to let it work with both the PHP and Java version of OW2 RUBiS.
You can select what version of OW2 RUBiS to use by the new 'rubis.incarnation' configuration parameter.

Also,
- I've tried to make the driver more compliant with the native client `edu.rice.rubis.client.ClientEmulator`,
- I've implemented all 27 operations + 2 special operations (i.e., "Back to Previous Page" and "End of Session"), provided by the original RUBiS version as well,
- I've changed the traffic matrices to be more compliant with the OW2 RUBiS, and
- I've added several configuration options to provide more flexibility on the user side.

See:
https://github.com/sguazt/rain-workload-toolkit/tree/wkl-rubis-compliant/src/radlab/rain/workload/rubis/README.md
for a description of the new configuration parameters.

Please, consider to merge this branch.

Best,

-- Marco