CiscoNexus: Update and Remove deprecated vars
Backward compatible backport (modified by hand).
Update and Remove deprecated variables from Cisco Nexus Config.
* Deprecated variables include vlan_name_prefix, svi_round_robin,
provider_vlan_name_prefix, persistent_switch_config,
never_cache_ssh_connection, ssh_port, switch_replay_count,
nexus_driver, and host_key_checks.
* Change config replay to on by defaulting switch_heartbeat_time=30.
* Replaced method of configurating host_ports_mapping config.
Change-Id: Iee2f869c4054f1120d224994aba8c827f981e6c0
Closes-bug: #1793379
(cherry picked from commit f45169f38d)
b0196fd0e4