Use .zeek file suffix in unit tests

testing/btest/language/nested-sets.zeek

@@ -0,0 +1,19 @@
+# @TEST-EXEC: for i in `seq 21`; do echo 0 >> random.seed; done
+# @TEST-EXEC: test `bro -b -G random.seed %INPUT` = "pass"
+
+type r: record {
+	b: set[count];
+};
+
+global foo: set[r];
+global bar = set(1,3,5);
+
+add foo[record($b=bar)];
+
+bar = set(5,3,1);
+delete foo[record($b=bar)];
+
+if ( |foo| > 0 )
+	print "fail";
+else
+	print "pass";