Upgrade to netty 4.0.21

Open Tasks:

- Decide what to do with shared-event-executor (src/riemann/transport.clj).

The shared-event-executor is replacing the old thread pool (because it was
deprecated).
But there might be a better implementation available which gives you a similar
degree of control.

This should probably be addressed before the next release of riemann.

The current value is set to 100 (100 available threads) using the
DefaultEventExecutorGroup.

- Test cases might be misbehaving.

riemann.graphite-test seems to be displaying an error which might be
a programming error. An exception that is not being caught by implemention the
correct pipeline event handler.

I'm not sure how to address this.
Added Datadog plugin
Fix example and add a hint

Fix the first example and add a hint about where to get the token from. The webhook_uri support still isn't working right, but this should be a decent work around for anyone trying to use this module for now.
streams/sdo: Special case for 0 and 1 arg versions

This changes sdo to have special cases for 0 and 1 args, calling
bit-bucket in the 0-arg case, and the child directly in the second case.

Fixes #398.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Add OpenTSDB server support

Consume OpenTSDB datapoints and convert them into Riemann events.

This work was mostly based on `riemann.transport.graphite`, as the
concept is very similar.
Merge pull request #465 from iggy/patch-1

Fix example and add a hint
Merge pull request #469 from algernon/f/sdo-special-cases

streams/sdo: Special case for 0 and 1 arg versions
Merge pull request #470 from pharaujo/opentsdb_server

Add OpenTSDB server support
Remove unused leiningen build parser task
Indexes correctly persist through reloads.

Prior to this commit, the old index would be preserved correctly by the
core on reload, but the new set of streams would have a reference to a
*different* index. Just like config/service, config/index needs to check
for equivalency and return the current core's index if core/merge will
preserve it.

I believe this also fixes #473
Update service-equiv tests for indices

wrapped/unwrapped index are not equivalent.
Merge pull request #451 from pradeepchhetri/datadog

Added Datadog plugin
Merge pull request #432 from udoprog/netty-4

Upgrade to netty 4.0.21
Port OpenTSDB server to Netty 4

Also add round-trip tests for the OpenTSDB server. Noticed that wow,
this thing doesn't round-trip well. Not sure if this is intentional;
I'll defer to folks who understand the opentsdb data model better.
Graphite server roundtrip test
formatting
Netty 4.0.24.Final
Shrink netty executor to 1 thread per core, not 100.
Parallelize TCP worker/boss group shutdown

Speeds up the netty core tests.
Shut down TCP/UDP event executors faster

Cut the quiet period to 10ms, which shaves about 30s off the test suite
runtime.