Merge dictionaries when extending CI builds

When one CI build YAML spec extended another, the `reproduce_ci_env.py`
script was overwritting local configuration with the configuration being
extended. This change merges all configuration together (which appears
to be how the GitLab CI works).

Utilities/CI/reproduce_ci_env.py

@@ -57,6 +57,21 @@ def load_ci_file(ci_file_path):
           ci_state.update(yaml.safe_load(open(include_path)))
   return ci_state
 
+# Recursively updates the target dictionary with the source dictionary.
+# By recursive, I mean that if source contains a sub-dictionary that
+# target also contains, the target sub-dictionary is updated rather than
+# replaced. Likewise for sub-sub-dictionaries and so on. This code is
+# taken from StackOverflow:
+#   https://stackoverflow.com/questions/3232943/update-value-of-a-nested-dictionary-of-varying-depth
+def recursive_dictionary_update(target, source):
+  import collections.abc
+  for key, value in source.items():
+    if isinstance(value, collections.abc.Mapping):
+      target[key] = recursive_dictionary_update(target.get(key, {}), value)
+    else:
+      target[key] = value
+  return target
+
 def flattened_entry_copy(ci_state, name):
   import copy
   entry = copy.deepcopy(ci_state[name])
@@ -64,13 +79,11 @@ def flattened_entry_copy(ci_state, name):
   #Flatten 'extends' entries, only presume the first level of inheritance is
   #important
   if 'extends' in entry:
-    to_merge = []
-
     if not isinstance(entry['extends'], list):
       entry['extends'] = [ entry['extends'] ]
 
     for e in entry['extends']:
-      entry.update(ci_state[e])
+      recursive_dictionary_update(entry, ci_state[e])
     del entry['extends']
   return entry