Automated tests for list append.

Test the case of appending to a list and appending to a nonexistent
list (should error).

test/rules/list_append.yaml

@@ -0,0 +1,12 @@
+- list: my_list
+  items: [not-cat]
+
+- list: my_list
+  append: true
+  items: [cat]
+
+- rule: Open From Cat
+  desc: A process named cat does an open
+  condition: evt.type=open and proc.name in (my_list)
+  output: "An open was seen (command=%proc.cmdline)"
+  priority: WARNING

test/rules/list_append_failure.yaml

@@ -0,0 +1,3 @@
+- list: my_list
+  items: [not-cat]
+  append: true

test/rules/list_append_false.yaml

@@ -0,0 +1,12 @@
+- list: my_list
+  items: [cat]
+
+- list: my_list
+  append: false
+  items: [not-cat]
+
+- rule: Open From Cat
+  desc: A process named cat does an open
+  condition: evt.type=open and proc.name in (my_list)
+  output: "An open was seen (command=%proc.cmdline)"
+  priority: WARNING