test: Poll pageserver availability more aggressively at test startup

Even with the 100 ms interval, on my laptop the pageserver always
becomes available on second attempt, so this saves about 900 ms at
every test startup.

test_runner/fixtures/neon_fixtures.py

@@ -2553,7 +2553,7 @@ def poll_node_status(
         desired_availability: Optional[PageserverAvailability],
         desired_scheduling_policy: Optional[PageserverSchedulingPolicy],
         max_attempts: int,
-        backoff: int,
+        backoff: float,
     ):
         """
         Poll the node status until it reaches 'desired_scheduling_policy' and 'desired_availability'
@@ -2948,7 +2948,7 @@ def start(
             self.id
         ):
             self.env.storage_controller.poll_node_status(
-                self.id, PageserverAvailability.ACTIVE, None, max_attempts=20, backoff=1
+                self.id, PageserverAvailability.ACTIVE, None, max_attempts=200, backoff=0.1
             )
 
         return self