[Enhancement] Simplify etcd configuration and use proper URL instead of using @ as separator

[unmarshall]

Feature (What you would like to be added):

When creating configuration to be used subsequently by etcd-backup-restore and etcd containers two properties, namely:
initial-advertise-peer-urls and advertise-client-urls use @ character to separate different parts of the URL. This is not really required. Other properties which also contain URLs use proper HTTP URL format namely: initial-cluster, listen-[client/peer]-urls. Using @ only complicates the usage with no added benefit.

Motivation (Why is this needed?):
Reduce the complexity where it is not needed.

Approach/Hint to the implement solution (optional):

[shreyas-s-rao]

/close by #812