We were seeing some rollover artifacts where something would be shut down so
a port could be re-used, but it was still being referenced by some running
thing. This gives more time before rolling over.
This patch removes the porter tool which hands out free ports from a
given range with a library which does the same thing. The challenge for
acquiring free ports in concurrent go test runs is that go packages are
tested concurrently and run in separate processes. There has to be some
inter-process synchronization in preventing processes allocating the
same ports.
freeport allocates blocks of ports from a range expected to be not in
heavy use and implements a system-wide mutex by binding to the first
port of that block for the lifetime of the application. Ports are then
provided sequentially from that block and are tested on localhost before
being returned as available.
