test: infamy: Make it easier to resolve mapped port names

The somewhat clumsy construct of resolving a logical port name to its
physical counterpart has been with us from Infamy's inception:

    _, physical_port = env.ltop.xlate(logical_node, logical_port)

This is needlessly verbose. Since devices already have access to the
mappings which applies to it, make them easy to access:

    target = env.attach("target")

    # Get physical port names via the subscript operator
    target["data0"]

test/infamy/restconf.py

@@ -119,6 +119,7 @@ class Device(Transport):
 
         self.name = name
         self.location = location
+        self.mapping = mapping
         self.url_base = f"https://[{location.host}]:{location.port}"
         self.restconf_url = f"{self.url_base}/restconf"
         self.yang_url = f"{self.url_base}/yang"

test/infamy/transport.py

@@ -55,6 +55,9 @@ class Transport(ABC):
     def call_action(self, xpath):
         pass
 
+    def __getitem__(self, key):
+        return self.mapping[key]
+
     def get_iface(self, name):
         """Fetch target dict for iface and extract param from JSON"""
         content = self.get_data(infamy.iface.get_xpath(name))