Move mark comparision into ZuulMark object

A ConfigurationError object makes a ConfigurationErrorKey from
<context, mark, error-string>.  The ConfigurationErrorKey assumes the
"mark" argument is a ZuulMark object that has fields such as "line"
and "snippet".

However there is a path to set config errors via
QueueItem.setConfigError(string) which makes a ConfigurationError with
<None, None, error-string>.  Consequently the "mark" object in the
ConfigurationErrorKey isn't actually a ZuulMark and the __eq__
comparision for ConfigurationErrorKey objects can fail.

This can hit in PipelineManager._findRelevantErrors() which walks the
error list and ends up doing a comparision with

  if ((err.key not in
       parent_layout.loading_errors.error_keys)

I think the result in production is that you can get a range of errors
that do not get reported.  I came to looking at this because I
accidentally added Ansible playbooks under .zuul.d and something was
clearly wrong, but I was not getting any error messages.

The solution here is to move the field matching for the ZuulMark into
an __eq__ method in the ZuulMark object itself, allowing None to be a
valid value.

Adding a file that looks like a playbook triggers this path for the
test_dynamic_split_config test, which passes with this fix.

Change-Id: If59f5556141db4bda54a61b459ffbffb935094ae

tests/fixtures/config/split-config/git/org_project1/.zuul.d/playbooks/playbook.yaml

@@ -0,0 +1,8 @@
+# This file is just to induce a config error
+
+- hosts: all
+  tasks:
+
+    - name: Debug
+      debug:
+        msg: 'Hello'

zuul/configloader.py

@@ -346,6 +346,10 @@ class ZuulMark(object):
             column=self.column + 1,
         )
 
+    def __eq__(self, other):
+        return (self.line == other.line and
+                self.snippet == other.snippet)
+
 
 class ZuulSafeLoader(yaml.SafeLoader):
     zuul_node_types = frozenset(('job', 'nodeset', 'secret', 'pipeline',

zuul/model.py

@@ -128,8 +128,7 @@ class ConfigurationErrorKey(object):
         if not isinstance(other, ConfigurationErrorKey):
             return False
         return (self.context == other.context and
-                self.mark.line == other.mark.line and
-                self.mark.snippet == other.mark.snippet and
+                self.mark == other.mark and
                 self.error_text == other.error_text)