Improve TCP related tests for dtrace.

Ensure that the TCP connections are terminated gracefully as expected
by the test. Use appropriate numbers for sent/received packets.
In addition, enable tst.localtcpstate.ksh, which should pass, but
doesn't until https://reviews.freebsd.org/D16369 is committed.

Reviewed by: markj@
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D16288

Adjust comment to reality since r286171.

Sponsored by: Netflix, Inc.

Fix shebangs and execute bit of test scripts.

Since we don't have /usr/bin/ksh, use a generic way of specifying
ksh. Some of the tests only run with ksh93, so use this shell
for these tests. Two of the tests don't have the execute bit set,
so fix this, too.

Reviewed by: markj@
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D16270

- Remove hardcoded paths for the perl executable.
- Rather than assuming that a process is listening on 127.0.0.1:22, use
nc(1) to find an available port and bind to it for the duration of the
test.

MFC after: 1 week
Sponsored by: EMC / Isilon Storage Division

tcp provider tests: sleep for a bit after closing the socket so that
libdtrace has a chance to capture the traced data.

MFC after: 1 week

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Port most of the DTrace tests to FreeBSD.

Sponsored by: The FreeBSD Foundation