Previously, the set_statsd_prefix method was used to mutate a logger's
StatsdClient tail prefix after a logger was instantiated. This pattern
had led to unexpected mutations (see Related-Change). The tail_prefix
can now be passed as an argument to get_logger(), and is then
forwarded to the StatsdClient constructor, for a more explicit
assignment pattern.
The set_statsd_prefix method is left in place for backwards
compatibility. A DeprecationWarning will be raised if it is used
to mutate the StatsdClient tail prefix.
Change-Id: I7692860e3b741e1bc10626e26bb7b27399c325ab
Related-Change: I0522b1953722ca96021a0002cf93432b973ce626
eda7d5fe3c