Use the same port selection method on all systems

Use the same port selection method on all systems

When system tests are run on Windows, they are assigned port ranges that
are 100 ports wide and start from port number 5000.  This is a different
port assignment method than the one used on Unix systems.  Drop the "-p"
command line option from bin/tests/system/run.sh invocations used for
starting system tests on Windows to unify the port assignment method
used across all operating systems.