Add a simple script which calls open(2) and others to generate events for

Add a simple script which calls open(2) and others to generate events for
testing.

This test times-out on a quiet system because there is nobody triggers
syscall::open:entry or syscall::: probe while test execution.

Reviewed by:	gnn, markj (earlier version)
Differential Revision:	https://reviews.freebsd.org/D11671