Move Events interface into Events package.

Signed-off-by: Johannes Tuchscherer <jtuchscherer@pivotallabs.com>
[#67664082] Add HeartbeatGenerator.

Signed-off-by: Johannes Tuchscherer <jtuchscherer@pivotallabs.com>
Add SetOrigin to emitter.Emitter interface.

Use pointers to events.Origin rather than a copy.

Signed-off-by: Johannes Tuchscherer <jtuchscherer@pivotallabs.com>
[#67664082] Begin heartbeat generation when emitting metrics.

Begin heartbeat generation when creating a instrumentedHandler or
an instrumentedRoundTripper.

Signed-off-by: Johannes Tuchscherer <jtuchscherer@pivotallabs.com>
[#67664082] Implement GetHeartbeatEvent in InstrumentedEmitter.

- Rename GetData to GetHeartbeatEvent.
- Make instrumentedEmitter type private
- Create NewTestEvent helper
- Rename DropsondeStatus to Heartbeat

Signed-off-by: caleb miles <cmiles@pivotallabs.com>
[#67664082] Don't allow empty jobName when emitting events.

Signed-off-by: caleb miles <cmiles@pivotallabs.com>
[#67664082] Regenerate protobuf source.

Signed-off-by: caleb miles <cmiles@pivotallabs.com>