format error messages from module_utils.basic nicer

* lists are printed as a string, separated by a comma and a space
* require_if tells if is_one_of was True or False

lib/ansible/module_utils/basic.py

@@ -1621,7 +1621,7 @@ class AnsibleModule(object):
         for check in spec:
             count = self._count_terms(check, param)
             if count > 1:
-                msg = "parameters are mutually exclusive: %s" % (check,)
+                msg = "parameters are mutually exclusive: %s" % ', '.join(check)
                 if self._options_context:
                     msg += " found in %s" % " -> ".join(self._options_context)
                 self.fail_json(msg=msg)
@@ -1645,7 +1645,7 @@ class AnsibleModule(object):
             non_zero = [c for c in counts if c > 0]
             if len(non_zero) > 0:
                 if 0 in counts:
-                    msg = "parameters are required together: %s" % (check,)
+                    msg = "parameters are required together: %s" % ', '.join(check)
                     if self._options_context:
                         msg += " found in %s" % " -> ".join(self._options_context)
                     self.fail_json(msg=msg)
@@ -1686,6 +1686,9 @@ class AnsibleModule(object):
             # present, else all requirements should be present.
             if is_one_of:
                 max_missing_count = len(requirements)
+                term = 'any'
+            else:
+                term = 'all'
 
             if key in param and param[key] == val:
                 for check in requirements:
@@ -1693,7 +1696,7 @@ class AnsibleModule(object):
                     if count == 0:
                         missing.append(check)
             if len(missing) and len(missing) >= max_missing_count:
-                msg = "%s is %s but the following are missing: %s" % (key, val, ','.join(missing))
+                msg = "%s is %s but %s of the following are missing: %s" % (key, val, ', '.join(missing))
                 if self._options_context:
                     msg += " found in %s" % " -> ".join(self._options_context)
                 self.fail_json(msg=msg)