[show]fix for show muxcable status by replacing "hostname" to "peer_switch" for deriving tor ipv4_address (#1360)

This PR provides the support for fixing the show muxcable config.
There was a change in the Config_DB schema where there was an addition of key-value pair
"peer_switch:tor_name" in DEVICE_METADATA|localhost table which actually gives the other TOR's name (hostname).
This TOR name is then utilized in PEER_SWITCH|switchname table which has "address_ipv4: IPv4 address" key-value pair,
which correctly gives the ip address for displaying on the show mux config

What is the motivation for this PR?
To add the fix the working for show muxcable config

Signed-off-by: vaibhav-dahiya <vdahiya@microsoft.com>

Author: vdahiya12

show/muxcable.py

@@ -63,7 +63,7 @@ def get_switch_name(config_db):
     info_dict = config_db.get_entry("DEVICE_METADATA", "localhost")
     #click.echo("{} ".format(info_dict))
 
-    switch_name = get_value_for_key_in_dict(info_dict, "localhost", "hostname", "DEVICE_METADATA")
+    switch_name = get_value_for_key_in_dict(info_dict, "localhost", "peer_switch", "DEVICE_METADATA")
     if switch_name is not None:
         return switch_name
     else:

tests/mock_tables/config_db.json

@@ -666,6 +666,7 @@
         "hwsku": "Mellanox-SN3800-D112C8",
         "mac": "1d:34:db:16:a6:00",
         "platform": "x86_64-mlnx_msn3800-r0",
+        "peer_switch": "sonic-switch",
         "type": "ToRRouter"
     },
     "DEVICE_NEIGHBOR|Ethernet4": {