xstat: use ephemeral ports for xstat_fs_test and scout

xstat: use ephemeral ports for xstat_fs_test and scout

Instead of trying to bind to port 7101, and then retrying if
the port is in already in use, let the os find an available
port for scout and xstat_fs_test.

This fixes a bug where scout and xstat_fs_test do not call
rx_Finalize() before retrying rx_Init() with a different port
number, causing the program to crash later when more than
one copy of xstat_fs_test and/or scout are running at the same
time.

Change-Id: I64e4916b03b1cae20ef36bb1ae293885962677e7
Reviewed-on: http://gerrit.openafs.org/10707
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>