Add an auxiliary subroutine to generate some events for testing

This test is also timeout on a quiet system because there is nobody triggering
read probefunc while test execution.

Reviewed by:	gnn, markj, ngie
Differential Revision:	https://reviews.freebsd.org/D11731

cddl/contrib/opensolaris/cmd/dtrace/test/tst/common/dtraceUtil/tst.ZeroFunctionProbes.d.ksh

@@ -39,6 +39,15 @@
 ##
 
 
+reader()
+{
+	while true
+	do
+		sleep 0.1
+		cat /etc/motd > /dev/null
+	done
+}
+
 if [ $# != 1 ]; then
 	echo expected one argument: '<'dtrace-path'>'
 	exit 2
@@ -46,6 +55,9 @@ fi
 
 dtrace=$1
 
+reader &
+child=$!
+
 $dtrace -qZf wassup'{printf("Iamkool");}' \
 -qf read'{printf("I am done"); exit(0);}'
 
@@ -55,4 +67,6 @@ if [ "$status" -ne 0 ]; then
 	echo $tst: dtrace failed
 fi
 
+kill $child
+
 exit $status