test.sh: Sort out netcat zoo

test.sh: Sort out netcat zoo

The previous code distinguished between Linux and non-Linux netcat.
This didn't stand the test of time, since Linux distributions now ship
multiple variants of netcat and other operating systems also provide
multiple options.  So instead try to detect the variant from the help
output.  Also, the previous uses of the -q and -w options behaved
strangely with some versions and/or were inconsistent with the
documentation.  So abandon those options and just rely on the existing
killall call.

The test_server_connect_timeout_establish test should now pass again on
hopefully most configurations.