[COMMON][ETCD] Skip startup self-discovery for etcd nodes

[COMMON][ETCD] Skip startup self-discovery for etcd nodes

Current startup script of etcd checks whether all assumed other nodes
are already running, before proceeding. This check, however, also
includes checking localhost, but due to using headless service
statefulset pod DNS discovery, it doesnt succeed immediately.
In some deployments k8s DNS server may be laggy, thus failing startup
script to finish before liveness check. This patch fixes such failures
of 1 pod etcd clusters, and improves startup time for any size ones.

Signed-off-by: Konrad Bańka <k.banka@samsung.com>
Issue-ID: OOM-2668
Change-Id: I2f9263a0f4964b0a495631775d0cbbceef25e85b