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