move DefaultEmitter creation into dropsonde.Initialize()

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
Renamed helpers -> factories and factored out test_helpers.

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
Added TcpEmitter.

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
initialize default heartbeat emitter

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
eliminate DefaultAddress package variable in UdpEmitter

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
Factor out InstrumentedEmitter interface

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
Callers check dropsonde.Initialize() error result

Signed-off-by: Johannes Petzold <jpetzold@pivotallabs.com>
Set origin at emitter New instead of via SetOrigin

Signed-off-by: John Tuley <jtuley@pivotallabs.com>
Clean up origin creation in tests

Signed-off-by: John Tuley <jtuley@pivotallabs.com>