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, and configuration, as *-previous before replacement. Only one copy is maintained to limit disk usage.

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