Allow GCE firewall rules to be updated when attributes changes. Fixes #2111.

Previously, when the attributes of a GCE firewall change, they were ignored.  This PR changes that behavior and now updates them.

Note that the "update" also removes attributes that are not specified.

An overview of the firewall rule behavior is as follows:

1. firewall name in GCP, state=absent in PLAYBOOK: Delete from GCP
2. firewall name in PLAYBOOK, not in GCP: Add to GCP.
3. firewall name in GCP, name not in PLAYBOOK: No change.
4. firewall names exist in both GCP and PLAYBOOK, attributes differ: Update GCP to match attributes from PLAYBOOK.

lib/ansible/modules/cloud/google/gce_net.py

@@ -34,6 +34,7 @@ options:
   allowed:
     description:
       - the protocol:ports to allow ('tcp:80' or 'tcp:80,443' or 'tcp:80-800;udp:1-25')
+        this parameter is mandatory when creating or updating a firewall rule
     required: false
     default: null
     aliases: []
@@ -246,12 +247,48 @@ def main():
 
             allowed_list = format_allowed(allowed)
 
+            # Fetch existing rule and if it exists, compare attributes
+            # update if attributes changed.  Create if doesn't exist.
             try:
-                gce.ex_create_firewall(fwname, allowed_list, network=name,
+                fw_changed = False
+                fw = gce.ex_get_firewall(fwname)
+
+                # If old and new attributes are different, we update the firewall rule.
+                # This implicitly let's us clear out attributes as well.
+                # allowed_list is required and must not be None for firewall rules.
+                if allowed_list and (allowed_list != fw.allowed):
+                    fw.allowed = allowed_list
+                    fw_changed = True
+
+                if src_range != fw.source_ranges:
+                    fw.source_ranges = src_range
+                    fw_changed = True
+
+                if src_tags != fw.source_tags:
+                    fw.source_tags = src_tags
+                    fw_changed = True
+
+                if src_tags != fw.target_tags:
+                    fw.target_tags = target_tags
+                    fw_changed = True
+
+                if fw_changed is True:
+                    try:
+                        gce.ex_update_firewall(fw)
+                        changed = True
+                    except Exception as e:
+                        module.fail_json(msg=unexpected_error_msg(e), changed=False)
+
+            # Firewall rule not found so we try to create it.
+            except ResourceNotFoundError:
+                try:
+                    gce.ex_create_firewall(fwname, allowed_list, network=name,
                         source_ranges=src_range, source_tags=src_tags, target_tags=target_tags)
-                changed = True
-            except ResourceExistsError:
-                pass
+                    changed = True
+
+                except Exception as e:
+                    module.fail_json(msg=unexpected_error_msg(e), changed=False)
+
             except Exception as e:
                 module.fail_json(msg=unexpected_error_msg(e), changed=False)
 
@@ -279,17 +316,13 @@ def main():
             network = None
             try:
                 network = gce.ex_get_network(name)
-#                json_output['d1'] = 'found network name %s' % name
+
             except ResourceNotFoundError:
-#                json_output['d2'] = 'not found network name %s' % name
                 pass
             except Exception as e:
-#                json_output['d3'] = 'error with %s' % name
                 module.fail_json(msg=unexpected_error_msg(e), changed=False)
             if network:
-#                json_output['d4'] = 'deleting %s' % name
                 gce.ex_destroy_network(network)
-#                json_output['d5'] = 'deleted %s' % name
                 changed = True
 
     json_output['changed'] = changed