Choosing a port in advance is racy. A better solution is to use a Unix Domain
socket in the per-etcd-instance data directory. Then the name can be determined
in advance and there's no risk of conflicts with other etcd instances.
With unix:// for the endpoint, we have to be a bit more careful about
passing a TLS config to the etcd client library because for unix://, in
contrast to http://, it tries to use an incomplete config which
then fails to establish the connection.
This provides a mechanism for overriding the forced increase of the klog
verbosity to 4 when starting the apiserver and uses that for the scheduler_perf
benchmark. Other tests run as before.
A global variable was used because adding an explicit parameter to several
helper functions would have caused a lot of code churn (test ->
integration/util.StartApiserver ->
integration/framework.RunAnAPIServerUsingServer ->
integration/framework.startAPIServerOrDie).
The apiserver may be configured to generate the Service
kubernetes.default and its endpoints addresses.
This service is single-stack, hence, the endpoints and the ClusterIP
must have the same IP family.
