ADD rpm-ts (timstamped) target

This new rpm target (that will probably use mainly at jenkins) is for easying the work in QA and integration, so now a precise version is used for each generated RPM, instead of using "0.14.0-next" for all them along the same month more or less.

E.g.

```
<orion>
  <version>0.14.0_20140606121049</version>
  <uptime>0 d, 0 h, 0 m, 29 s</uptime>
  <git_hash>327813b4262357895d7d4a96ecceea1f10aec16d</git_hash>
  <compile_time>nodate</compile_time>
  <compiled_by>fermin</compiled_by>
  <compiled_in>centollo</compiled_in>
</orion>

[fermin@centollo fiware-orion]$ /usr/bin/contextBroker --version
0.14.0_20140606121049
Copyright 2013 Telefonica Investigacion y Desarrollo, S.A.U
Orion Context Broker is free software: you can redistribute it and/or
modify it under the terms of the GNU Affero General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.

Orion Context Broker is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero
General Public License for more details.

Telefonica I+D
```
I don't like this approach... but with my knowledgue on RPM tooling is the only that I've been able to make work in a reasonable ammount of time :)