Make StatsD tests less flaky.
Make StatsD tests less flaky.

There have been a bunch of Jenkins failures lately where the StatsD
tests fail because they can't bind to their desired port. There's
nothing special about the particular port they're using, so now we let
the kernel pick an available one for us.

This also lets us get rid of a sleep() in the test that looked like an
attempt to alleviate EADDRINUSE errors, so now in the happy case, the
tests are a few fractions of a second faster.

Change-Id: Idee11349254107a59643539b1566f3588eee7ef4

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