tracing: Add hist trigger onchange() handler test case

Add a test case verifying the basic functionality of the
hist:onchange($var) handler.

Link: http://lkml.kernel.org/r/bec87aa8ed7d81794510b3d465096a750c71fce7.1550100284.git.tom.zanussi@linux.intel.com



Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>