If a users chooses to disable the Alertmanager cluster feature, there is
no cluster name nor cluster peers. Hence these should be optional. Only
cluster status is set to "disabled".
Signed-off-by: Max Leonard Inden <IndenML@gmail.com>
When users start Alertmanager with `--cluster.listen-address=`, the
cluster will not be initialized, hence api.peer will be `nil`. So far
this would result in a nil pointer dereference by the API v2 accessing
the api.peer field.
With this patch, api v2 skips populating the peers array, sets the name
to an empty string and the status to "disabled" in case `api.peer` is
nil.
Signed-off-by: Max Leonard Inden <IndenML@gmail.com>
