DRIVERS-3426: Use documented 'auth_database' field instead 'db' for initial-dns-seedlist-discovery tests

Author: sanych-sun

source/initial-dns-seedlist-discovery/tests/replica-set/dbname-with-commas-escaped.json

@@ -10,4 +10,4 @@ options:
   replicaSet: repl0
   ssl: true
 parsed_options:
-  defaultDatabase: some,db
+  auth_database: some,db

source/initial-dns-seedlist-discovery/tests/replica-set/dbname-with-commas-escaped.yml

@@ -10,4 +10,4 @@ options:
   replicaSet: repl0
   ssl: true
 parsed_options:
-  defaultDatabase: some,db
+  auth_database: some,db

source/initial-dns-seedlist-discovery/tests/replica-set/dbname-with-commas.json

@@ -11,7 +11,7 @@ options:
 parsed_options:
     user: "b*b@f3tt="
     password: "$4to@L8=MC"
-    db: "mydb?"
+    auth_database: "mydb?"
 # Don't run a ping for URIs that include userinfo. Ping doesn't require authentication, so missing
 # userinfo isn't a problem, but some drivers will fail handshake on a connection if userinfo is
 # provided but incorrect.