DiscoveryClient - Add awareness of Discovery Service's Cluster ID environment variable (#242)

* Update DiscoveryClient to look for the NIDiscovery_ClusterId environment variable (used by the Discovery Service for initializing its cluster ID) to determine whether the key file exists to indicate an already launched Discovery Service.

* Review feedback - use SNAKE_CASE for environment variable name

Signed-off-by: Hunter Kennon hunter.kennon@emerson.com

Author: hunter-ni

packages/ni.measurementlink.discovery.v1.client/src/ni/measurementlink/discovery/v1/client/_support.py

@@ -31,7 +31,8 @@
 
 
 def _get_discovery_service_address() -> str:
-    key_file_path = _get_key_file_path()
+    cluster_id = os.environ.get("NIDISCOVERY_CLUSTERID")
+    key_file_path = _get_key_file_path(cluster_id)
     _ensure_discovery_service_started(key_file_path)
     _logger.debug("Discovery service key file path: %s", key_file_path)
     with _open_key_file(str(key_file_path)) as key_file: