Finishing touches on RPM generation

The first part of this PR switches RPM from a plain call to cmake to using the %cmake macro defined in RPM. This ensures that all of the platform's default flags are passed to cmake. Some of the paths that were defined needed to be undefined to ensure that plain cmake packages still install to the same directories as in debians. There are a couple of other touch-ups in the spec template as well.

The second part makes RPM generation display a warning instead of failing outright if no RPM platforms are listed in the release platforms of rosdep for the distribution. It also enables RPM generation by default in the list of actions used by new configurations.

This means that current packages will need to update their `tracks.yml` if they wish to enable RPM generation.

I have expanded the proof-of-concept that I created in (https://github.com/ros-infrastructure/bloom/pull/228) to include all of ROS Hydro and Indigo. The packages were up-to-date as of ~~yesterday (6/5/2014)~~ **EDIT:** 6/7/2014

I have successfully packaged 95% of ROS Hydro and 99% of Indigo using this generator. I encourage anyone who is interested to check out the packages and the buildfarm. Note that the "public" repository is not yet used, only "building" and "shadow-fixed".

- Hydro Build Status: http://csc.mcs.sdsmt.edu/ros/rpmbuild/hydro.html
- Indigo Build Status: http://csc.mcs.sdsmt.edu/ros/rpmbuild/indigo.html
- Buildfarm: http://csc.mcs.sdsmt.edu/jenkins/
- Repositories: http://csc.mcs.sdsmt.edu/ (links at the bottom)

RPM generation will not happen until Fedora is added to the release platforms. When that happens, this PR will start doing its job. It can, however, be merged and released before that time without consequence.

Thanks much,

--scott
Can you use `sys.exit(0)` here? That way it is consistent with the rest of the code base.