Document CONTAINERS_CONF/CONTAINERS_STORAGE_CONF Env variables

Also Switch to using CONTAINERS_REGISTRIES_CONF for registries.conf
overrides.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

test/python/docker/__init__.py

@@ -39,7 +39,7 @@ class Podman(object):
         self.cmd.append("--root=" + os.path.join(self.anchor_directory, "crio"))
         self.cmd.append("--runroot=" + os.path.join(self.anchor_directory, "crio-run"))
 
-        os.environ["REGISTRIES_CONFIG_PATH"] = os.path.join(
+        os.environ["CONTAINERS_REGISTRIES_CONF"] = os.path.join(
             self.anchor_directory, "registry.conf"
         )
         p = configparser.ConfigParser()
@@ -50,7 +50,7 @@ class Podman(object):
                 "registries.block": {"registries": "[]"},
             }
         )
-        with open(os.environ["REGISTRIES_CONFIG_PATH"], "w") as w:
+        with open(os.environ["CONTAINERS_REGISTRIES_CONF"], "w") as w:
             p.write(w)
 
         os.environ["CNI_CONFIG_PATH"] = os.path.join(