Update rtdev-* Scripts and README to Reflect Latest Riak Versions

- Change the supported version of Riak to be 1.3.2, 1.4.10 and 2.0.0
- Add Erlang R16B02 for 2.0.0 and drop R14B04
- Fix upgrade test run instructions
- Build `stagedevrel` instead of `devrel`
- Add the optional `$RT_CURRENT_TAG` to specify which tag to pull when setting up `current`
- Add the optional `$RT_USE_EE` to pull from the `riak_ee` git repository instead of `riak`
- Pull all versions from git instead of old releases from AWS (to allow EE versions)
- Quit redirecting all cloning and building output to `/dev/null`
- If using the EE version, the oldest version is 1.3.4, not 1.3.2 like it is for OS
I'd be in favor of not dumping the git output or just sending it to a file. Running `rtdev-all.sh` there was tons of git output and I had to scroll back pretty far to see the build output.