add stub for getting the metrics directory
write the unit test, TDD FTW
implement fetching the configuration such that the unit test passes
more TDD: ensure metrics_directory is part of the ReceiverConfig object
implement metrics directory being part of the ReceiverConfig
TDD: stub for getting the metrics file
test for getting the metrics file
implementation of get_metrics_file
copy and paste _write_metrics and _reset_metrics from the broadcaster

cc @mriehl : perhaps this could go into yadtcommons
stub for write_metrics_to_file
global METRICS dict
test for having the Receiver write metrics
make write_metrics_to_file work and fix test
rename metrics test
simplify test, with correct use of patch.dict
adding stubs for the next tests
code and tests for abort and creating directory
remove unused comment
fix naming scheme, ybc => yrc
fix code to match test