Add success case test

Author: smklein

dev-tools/omdb/tests/successes.out

@@ -1,3 +1,16 @@
+EXECUTING COMMAND: omdb ["db", "db-metadata", "ls-nexus"]
+termination: Exited(0)
+---------------------------------------------
+stdout:
+Target Blueprint ......<REDACTED_BLUEPRINT_ID>....... @ nexus_generation: 1
+ID                                   |LAST_DRAINED_BLUEPRINT |STATE  |TRANSITIONING_TO 
+-------------------------------------+-----------------------+-------+-----------------
+..........<REDACTED_UUID>........... |n/a                    |active |                 
+---------------------------------------------
+stderr:
+note: using database URL postgresql://root@[::1]:REDACTED_PORT/omicron?sslmode=disable
+note: database schema version matches expected (<redacted database version>)
+=============================================
 EXECUTING COMMAND: omdb ["db", "disks", "list"]
 termination: Exited(0)
 ---------------------------------------------

dev-tools/omdb/tests/test_all_output.rs

@@ -177,6 +177,7 @@ async fn test_omdb_success_cases(cptestctx: &ControlPlaneTestContext) {
     let mut output = String::new();
 
     let invocations: &[&[&str]] = &[
+        &["db", "db-metadata", "ls-nexus"],
         &["db", "disks", "list"],
         &["db", "dns", "show"],
         &["db", "dns", "diff", "external", "2"],