tests: Speed up IPC tests, especially on FreeBSD

After much discussion on IRC it was decided that 70000 iterations
of the stress patch didn't achieve anything significant over a
reasonable but smaller number. So it has been reduced to 5000 on
all platforms.

This patch also fixes a bug where test_ipc_disconnect_after_created
committed a use-after-free which could cause a crash on FreeBSD-devel.