podman-etcd: preserve containers for debugging

This change modifies the agent to keep stopped containers for log
inspection and debugging, with supporting changes to enable this
behavior.

• Conditionally reuse existing containers when configuration unchanged
• Move etcd inline configuration flags to external file to allow restarts without container recreation (mainly for the force-new-cluster flag)
• Archive previous container renaming it into *-previous, and its configuration files into /var/lib/etcd/config-previous.tar.gz archive. The tar.gz archive consists in:
  • the pod manifest created by CEO, used to generated the Etc configuration file
  • the Etcd configuration file
  • the auth json file Only one copy is maintained to limit disk usage.
• Both configuration and backup files location is configurable with 2 new input arguments.

Signed-off-by: Carlo Lobrano <c.lobrano@gmail.com>