The inboundPort settings of the first node in the group dictated the firewall configuration. Subsequent nodes added to the group had their inboundPort settings ignored.
GCE firewalls specify their "target" (VM instances) by means of tags - if a targetTag on a firewall matches the tag on an instance, the firewall's rules are allowed for the instance. This commit applies a tag for each requested inboundPort to new instances. Then, a firewall is created for each tag (if one does not already exist) which has 'allow' rules for the port.
Note - there is no GoogleComputEngineSecurityGroupExtensionExpectTest,
due to it being more or less redundant given that we're not making any
new API calls.
Does not include aggregated list method calls, due to those calls not
working with service accounts.
Does not include image insert or deprecate due to the extremely
complex system for creating images in GCE, which makes writing tests
for that a pain. Will come in a later commit.