tests: accomodate some messages that can fail tests (#8144)

## Problem

- `test_storage_controller_many_tenants` can fail with warnings in the
storage controller about tenant creation holding a lock for too long,
because this test stresses the machine running the test with many
concurrent timeline creations
- `test_tenant_delete_smoke` can fail when synthetic remote storage
errors show up

## Summary of changes

- tolerate warnings about slow timeline creation in
test_storage_controller_many_tenants
- tolerate both possible errors during error_tolerant_delete

test_runner/performance/test_storage_controller_scale.py

@@ -48,7 +48,16 @@ def test_storage_controller_many_tenants(
 
     # We will intentionally stress reconciler concurrrency, which triggers a warning when lots
     # of shards are hitting the delayed path.
-    env.storage_controller.allowed_errors.append(".*Many shards are waiting to reconcile")
+    env.storage_controller.allowed_errors.extend(
+        [
+            # We will intentionally stress reconciler concurrrency, which triggers a warning when lots
+            # of shards are hitting the delayed path.
+            ".*Many shards are waiting to reconcile",
+            # We will create many timelines concurrently, so they might get slow enough to trip the warning
+            # that timeline creation is holding a lock too long.
+            ".*Shared lock by TimelineCreate.*was held.*",
+        ]
+    )
 
     for ps in env.pageservers:
         # This can happen because when we do a loop over all pageservers and mark them offline/active,

test_runner/regress/test_tenant_delete.py

@@ -31,8 +31,12 @@ def error_tolerant_delete(ps_http, tenant_id):
             if e.status_code == 500:
                 # This test uses failure injection, which can produce 500s as the pageserver expects
                 # the object store to always be available, and the ListObjects during deletion is generally
-                # an infallible operation
-                assert "simulated failure of remote operation" in e.message
+                # an infallible operation.  This can show up as a clear simulated error, or as a general
+                # error during delete_objects()
+                assert (
+                    "simulated failure of remote operation" in e.message
+                    or "failed to delete" in e.message
+                )
             else:
                 raise
         else: